J.S.
My son also did this. I actually gave up because I was tired of disinfecting the bathroom 5 times a day. When he was closer to 3 he decided he wanted to go. I always let him see our family using the bathroom, and since he was the only one who wasn't, he wanted to be a big boy, too!
He still wouldn't poop in the potty, though. I struggled with this for several months, cleaning poop out of his underwear, until I told him in desperation one day that if he pooped in the potty he would get a piece of chocolate (since my daughter is extremely sugar-sensitive, chocolate is a huge treat in my house!). The very next time he pooped IN the potty, and has been doing so ever since.
My point is that every child is different. He may or may not be ready yet. You can keep trying, or you can decide to wait a little longer. You know your son best, and you know how you react best, too. If it's too frustrating, you may want to hold off for a while. If you're okay and it's really more important to get him trained, then by all means keep going!
Find out what presses your son's button. Is it candy? Stickers? Whatever works, offer it to him as a reward for a job well done!