C.F.
Since it will be summer soon,let him go w/o a diaper, if you have a backyard or a friend with one, camp out side for the day(s) with a potty seat, lunch, snacks, drinks, toys and games. If the pee runs down his leg, you don't have to clean the grass at least. This helps them associate the feeling with needing to use the potty. It is worth a try anyway.