I would make rules such as the bathroom and toilet are off limits.
He must use the diapers for both pee and poop and he must not ask for a diaper change.
The diaper checks should be random and the diaper changes should be done with the caregiver decide it's time to change them.
At home no pants or shorts and he must wear just the diaper, shirt and socks or just the diaper.
He must play with baby toys, sleep in a crib, suck on a pacifier, eat from a highchair, be fed and bottled fed.
He must watch baby cartoons and crawl around on the floor like a baby.
If I come up with some more rules I'll post again but that's all I have for now.