N.D.
The only thing i can say is just stop worrying and quite pushing so hard and he will do it himself. My little boy absolutely refused to use the potty at three and a half i was convinced he would be wearing pull ups in high school but everyone kept telling me to just leave him alone and he would do it when he was ready so one day i just stopped pushing. I didn't try to make him use the potty at all and then out of nowhere about two or three weeks later he just started going on his own and he had one accident about two weeks after that and hasn't had another since (he is four and a half now) other than that all i can say is good luck...