Can you wait and see if he gets the itchies and if he does, rather than give the shots, could you give him a steriod shot that would take care of his itchies and perhaps prevent them for a few more weeks? That might be enough to get you through the summer. Or he might need two of those, but it would still be easier than the alternative shots you described. I had a kitty that was allergic to something, I think we finally figured out it was food and certain kinds of litter, but when she would get these scabs and bumps all over her body, that's how it was treated until we found out what was causing it.