You could try a litter box with a cover or 'hood' while it's in the area you would prefer it not to be. (Or if you find a perfect-size Japanese screen or other decorative 'blind' at a garage sale, try that!)

However - I do hope it is as simple as a UTI and can be treated.

If it is behaviour - Medusa swears by Clomicalm!

As for enzyme cleaners - I'd ask the vet or a professional boarding kennel to recommend one - kitties' noses are much more sensitive than ours!