I don't know if it would work or not but try letting his daddy show him how he's suppose to sit down and go poopy. He likes standing up and peeing cuz his daddy does it, then daddy should show him how daddy poopies too. Or try making it fun, like giving him a reward when he goes poopy in the toilet, cuz he knows how right, he just won't. Give him a reward when he does, like a cookie or treat or something that he really likes. I'm about to go through the same thing with my youngest, but she's a girl. My oldest one almost had the same problem he knew how and where to use the potty, but we had him in pullups and knew they were like diapers, so he went in them anyway. So we just put him in regular underwear and he started using the bathroom cuz, he hated havin his underwear messy. Good luck, stay consecutive and have patience.