If he hasn't eaten in 4 weeks, he needs to eat. Some babies take f/t, some do not. Some will, then won't, then will again. I would offer a live rat pup. Also, not sure what size living quarters you have, but balls prefer small spaces. I usually start my babies out in shoeboxes. You may have to move him to something smaller to feed him, so he can't hide from the food. It's OK to leave a rat pup in overnight.