The litter I'm using has Cat Attract embeded in it, but I know there is a separate product you can buy. I could try that as well.
I had thought about asking the vet for an antianxiety medication for him to see if that would help him. It would have to be in shot form as he does not take pills at all. The vet tried to give him a steroid pill once (for a URTI) and he told me not to try, he's just not one of those kind of cats. I can give shots no problem, and the vet has showed me before how to give them (and I have lots of experiencing giving shots to humans)