You might find the stink less terrible if you can convince him to eat different food. I foster, so I meet a lot of cats, and have found that avoiding fishy foods and high carb foods (kibble) really helps make their poops less stinky.

I also have a different type of litter in the box in my bedroom because I’ve noticed that my cats don’t mind peeing in that litter, but will only poop in it if it’s the only box available.