M.L.
I would chart or make mental notes of his bowel movements while in your care. I know my son will have a b.m. at 10:00 a.m. You could almost set your watch by it LOL. I realized that was because we had breakfast at 9:15. When it was time to potty train, I would make sure I put him on the potty just before 10 and sure enough he went.
If you want to do a visual reward, I am not big on candy or food rewards, there are cute charts at childavenue.com. Maybe a sticker for each poppy on the potty.
Good luck!