We had a similar issue, with resisting pooping on the potty. He didn't really resist the potty, just pooping on the potty. My gut told me it was more physical difficulty than consciouse resistance. One thing kinda worked for us - We told DS that it was messy for him to poop in his pants, and so that when it was time for him to poop, he should tell us if he needs to go potty or have a diaper put on. (his choice)
It seemed to open up the communication a bit and give him a bit more control and power over the situation. Most importantly, it seemed to give him confidence. Once he started correctly identifying and communicating the sensation, we tried to guide him toward using the potty. When he would say it was time for a diaper, I would say that's great, why don't you sit on the potty while I get things ready so that you don't have an accident in your pants. If he had a special book he wanted to read, I would suggest reading the book, on the potty, prior to putting on the diaper. Once he relaxed, and pooped on the potty a couple of times, he pretty quickly moved to using the potty regularly.
It seemed physically easier for him to poop in a diaper than poop in the potty (his favorite pooping position was lying face down on the floor) so even after he was trained pretty well, if I could sense that he was having difficulty or noticed a change in his pattern, I would say something like "I know your a big boy and like to use the potty, but I think your body is having trouble pushing out the poop, and it's important that your body gets the poop out. Would it be OK if I put a diaper on you for a little while?" He would answer yes or no, again, his choice.
What surprised me, was that he didn't get confused at all. When wearing a diaper, he still told me when he had to go, or sometimes, he would look at me with a certain look in his eyes and say am I wearing a diaper? is it OK if I go in my diaper? While I would sometimes try to steer him to decide to use the potty, I tried to leave the choice to him.
As for incentives - once I knew he was able to physically accomplish the task (actually I started the incentive before I was confident he was physically able, but I regret that) we did have him complete a "star chart" for pooping. Every time he would poop on the potty, he would get a star. When he got X number of stars, he could "buy" a toy (A Thomas the Train car at our house!) I'm not sure it was necessary because I think once they start they tend to want to continue, but it was fun, it gave him a sense of accomplishment, and I'll definately do it again with DS#2.
In case you want to keep reading, I posted this to another thread yesterday, cut and paste to here with some edits...
My son started to potty train at about 36 months. I would say he is just now completing the process at 44 months. The main hold-up was pooping. At first, he didn't seem to get it. Didn't seem to recognize the sensation. Then he did recognize the sensation (reveled from body language, not verbal admission), but his innards would seem to tense up when he was on the potty (though he looked relaxed). There were a couple of times that we basically caught him in the act and carried him to the potty with a 'small tail', only to find that his body would 'suck it up' once on the potty. We would sing and read, he would ask me to read more....nothing worked. I did some on-line research and it seemed that this was not a rare thing. The suggestion is to ensure they are not constipated and if they are to fix that problem first (which it sounds like you've already done), and then basically be patient. As soon as my son did poop on the potty, it became pretty regular pretty fast, though he did have a phase where he still preferred to go in his pants. He preferred to poop while lying face down on the floor. We never really tried to control his timeline, though I think there were some 'power' issues involved. A couple of times I mentioned how he was now using the potty every time (a compliment, I thought!) and that seemed to trigger him to go back to going in his pants for a couple of days. I also noted that if he was at all under the weather, even a mild cold, that it seemed to interfer with potty training.