Sounds like you're doing everything right. No risk involved if you're watching him the entire time, then flipping him over. I feel his pain, I love sleeping on my belly... Just can't do so with my daughter in there lol.

I think he will be fine. just make sure his head isn't facing down and turned to the side mom. I use to do the same with my daughter.

If he can't flip himself, this seems very risky. Leave him on his back. A little gas is not worth the chance of suffocation.