The larger the cage, the longer you can go between full cleans -- I've heard of some people going six months between full cleans, but they have absolutely enormous cages and spot clean regularly, so it works out.
Hamsters actually naturally have pee areas in their burrows in the wild, so peeing in his house is a completely natural behaviour that you might not be able to train out of him. If he has a plastic house, I'd remove it and replace it with a wooden one with no floor, so the pee soaks down in to the substrate rather than sitting around in the plastic I'd also make sure the house is quite large, so that he can have an area to pee and an area to sleep in if he wants. Some people even provide multi chambered houses complete with little toilet for this
