J.R.
Maybe some love and logic? Does he tell you when he poops? If so, maybe saying "I"m sorry, what are you going to do about it?" Make it his responsibility since he made the decision to poop in the pants. I know you said you tried it, but try again without making a big fuss about him cleaning up his own mess. Just keep saying I'm sorry you pooped in your pants. There is toilet paper in the bathroom and I can get you a wet towel if you need, but I'm not wiping, then drop the subject and keep doing what you are doing. The other half of love and logic is to later say, I'd be happy to help you wipe when you poop in the potty. If he wakes up in the morning with poop in his pants, then just say I'm sorry, as before. Good luck with whatever works. Eventually it will come!