It's very common for some children to not poop on the toilet and yet be fine for going pee. So, some ideas...
Have him tell him you he needs to poop and give him a diaper to do it in.
or
Wait a while. It's okay. You've had a lot of posts on this, so much so that I do have to wonder if it's you who are ready instead of your child. If you are wanting to keep him peeing on the potty, then do offer a diaper for him to poop in. Otherwise, it's okay to take a step back and let him get a little more comfortable with all of it.
What I have noticed (as a nanny and teacher) was that kids who are stressed have a harder time using the toilet. Ina May Gaskin, in her book "Guide to Midwifery", talks about the unavoidable truth of "sphincter logic"; when the body is stressed, the sphincter muscles are contracted, thus nothing can pass. (Gaskin is referring to stalled labor here,but this holds true with any sphincter muscle.) However, when the person is relaxed, it is much easier to pass what needs to come out. Without going into detail, I have found this to be true with my own birth and then my recovery. (Most mothers who birthed vaginally will remember how traumatic their first bowel movement was after birthing ,especially if there was tearing. Now imagine you have NO IDEA about what's happening. That's what some kids experience.) When kids are stressed and upset, they have a much more difficult time pooping. In fact, with one family I worked with, the stakes felt so high that the child would regularly NOT poop on the toilet and then, within 15 minutes, poop in an inappropriate place when we was relaxed. (in his pants, on his tricycle, etc.) You can keep pressing it-- and possibly create a problem, or let it go. It's entirely up to you. Or, you can tell him "if you need a diaper for poop, let me know" and see what happens. I'm not trying to discourage you, but I agree with Dawn that if it's keeping you up at night, reconsider.