Hey L. Cowboy,
If my understanding of Jack manipulating is correct, it is only in the sense of taking opportunities as they presented themselves. I understand /read you as saying that Jack's ears perked a little when he heard Ennis all but say he was a virgin, the statement about not having had the "oppurtunity" a code word imo for not had sex , and that little hmmmm = Jack assessing the situation. Knows Ennis is way to far gone to attend to the sheep. tries to invite/coax Ennis into the tent where it's warmer. I saw no coercison,force or sneaky manipulative actions on Jack's part. The bedroll was big enough. Jack was right about what would happen when the fire died down cuz Ennis was practically an icicle when he woke up "hammering" his teeth together! Jack is awake, perhaps thinking that maybe Ennis wants to join him, but is afraid of his feelins and being that close to Jack in a bedroll, well...there maybe ...shall I say "effects" in that close proximity.
But Ennis was also flirting with Jack as he did a number of times throughout their stay on Brokeback, and Jack knew Ennis had some feelings of a romantic nature for him. In this way, you could say Ennis is manipulating Jack. It's harmless opportunity and nothing more. Check out the looks Ennis gives in this scenes leading up to FNIT. Is this flirting or what? It's very subtle at times , yet it's there.
Why DID Jack have to coax Ennis out of the cold into he tent anyway? ? Perhaps he was afraid of what he felt might happen imo. Yeah, he's drunk, but asked Jack for an extra blanket. He is making a concious decision to stay outside the tent.
Jack had to initiate this, Ennis was not going to, but perhaps wanted to. This was Jack's opportunity to give Ennis just a little "prompting" , a mind to ultimately reach Ennis in the most intimate way possible. So far I've seen Jack do nothing wrong, nothing in a pre-meditated, evil, destructive way. He simply made the most out of what was presented to him by fate or Ennis himself. Perhaps he read an "offer" in what Ennis spoke of earlier. In any case, He took the risk of his gut feeling about Ennis. He was correct . Once Ennis became a WILLING participant, the walls came down. The words manipulation/manipulate certainly has connotations, but in this case, only in the context of "oppotunity". Something much deeper was happening between them. Jack, the master at making something out of nothing wanted to express his feeling and wanted Ennis to be the one to express them with.
Opportunity knocked, Jack answered ,and Ennis walked in....freely.
My take.. 
Hi, aintfooling, Tony,
I agree that manipulator is a strong word, in the sense that it is associated with being manipulative, which has the much nastier connotation. And as Tony said, a better word is hard to find at the moment:
from online dictionaries:
1: to treat or operate with or as if with the hands or by mechanical means especially in a skillful manner
2 a: to manage or utilize skillfully b: to control or play upon by artful, unfair, or insidious means especially to one's own advantage
3: to change by artful or unfair means so as to serve one's purpose
1. to manage or influence skillfully, esp. in an unfair manner: to manipulate people's feelings.
2. to handle, manage, or use, esp. with skill, in some process of treatment or performance: to manipulate a large tractor.
3. to adapt or change (accounts, figures, etc.) to suit one's purpose or advantage.
And from the thesaurus:
http://thesaurus.reference.com/browse/manipulative artful, canny, careful, cautious, chary, circumspect, considerate, contriving, crafty, cunning, designing, devious, discreet, gingerly, guarded, guileful, intelligent, manipulative, politic, premeditating, safe, scheming, sharp, shrewd, sly, wary, wily
I am happy to replace the word manipulative with any one of the words cunning, scheming, or shrewd. However, it would detract from the irony of the manipulator being manipulated by the force of nature. Because in the end, that's what Jack said, "the short leash that you kept me on". He "felt" this so the relationship was in trouble.
I agree with aintfooling that Jack did not manipulate Ennis' feelings, only adapted to the situation to create FNIT. And Ennis was a willing participant, with the help of the whiskey of course, to make the tent scene inevitable. When you mix two lonely cowboys with a bottle of whiskey, put them in a small warm tent on a cold isolated mountain top, FNIT is just a natural consequence.
Is it predatory? NO! Is it unfair? NO! Is it selfish? Well...there must be at least a bit of self-serving interest on Jack's part. Let's be honest, he didn't do it just for Ennis. But that's neither wrong nor bad. It is simply his love for Ennis. He took the opportunity to allow Ennis to act on the same feelings in return. It is what made them as a couple complementary. Jack worked to make the relationship happen; Ennis worked to make Jack love him, with all the little things he did. Was that manipulative on Ennis' part? NO!
So, yes, I won't call Jack manipulative (except in the context of the irony of being manipulated by the force of nature) but instead refer to his shrewd assessment of their situation and his cunning arrangement of opportunities to make FNIT the beginning of their new chapter.
I don't know...I guess I am still confused by other demons in my own past that made the seduction by Jack of Ennis an issue, not of Jack, but the seduction itself.
As someone else said, Heath originally wanted the response by Ennis to be more violent and confrontational in FNIT. I think that would convey his own inner turmoil as well as his seeing through Jack's seduction, and saying, "don't try to manipulate me, let me come to this on my own." To me, Jack's most endearing quality is his patience with Ennis, waiting for the slow and steady to catch up with his own dreams and schemes, as in SNIT. The tragedy is that Ennis almost arrived at the gate of the little cow and calf operation when Jack died.
The tender scenes of Jack nursing little lambs in the mountain, carrying them across the river, caring for them, or just caressing one on horseback, show the same nurturing Jack who comforts Ennis whenever he is down. I think the tears and pain in the last scene is to mourn the passing of the best of these two characters, that will never come when their relationship ends. Soul-mates bring out the best in each other, and transform each others' faults by the power of love, as Ennis was transformed at the end, with Jack forever inside him.

Ennis+Jack

Thanks again for calling me on this, in your kind and gentle way.
