R.P.
My son was the exact same way!!! At first we thought he was constipated because he wouldn't go #2 for like 5 days. The Dr said it was alright to give him Miralax, like a teaspoon. We had to do that for like 6 weeks to get him regular. In that time she also said that if he asks for a diaper/pull up to go #2 then it was alright and really good if he asks. Pretty soon he just did it on the potty, I think more by accident than anything and that was it. He saw that it was not scary. What about at school? Does he use the potty at school? We also did the whole reward thing. I know some parents don't agree with it, but it worked for us. Anytime he went poop on the potty he got a present. This seems to be a REALLY common problem for boys.
Good luck