My FIV positive cat is licking all the fur off of his back. Possible remedies?

My FIV positive cat is licking the fur off of his back until the point that he bleeds. He is FIV positive (re: suppressed immune system) which excludes the possibility of steroid treatment. The vet has given us antihistamines and has proposed a reduction diet, neither of which seem to work. Anyone out there in a similar situation? Are there skin creams available for this problem? Any solution at all...Thanks!