Cat allergic to rabies vaccine--is he stuck?

I am very, very seriously considering continuing my studies in the UK, and as it would be for several years would want my cat to come with me. However, he is allergic to the rabies vaccine, and the measures that are normally taken to prevent the reaction are no good as he is allergic to them as well (I wasn't aware something could be allergic to Benadryl, but he nearly died from the reaction).
Has anybody run into this situation or know of someone who has? He is an indoors only cat so I am allowed to have him licensed in my city with a letter from his vet.
Thank you for any help you may be able to offer.

You could contact DEFRA to ask them:

Email
pettravel@ahvla.gsi.gov.uk

Pet Travel Scheme helpline
0370 241 1710

They might be able to offer an alternative option. Previously you had to wait 6 months after administering the vaccine before the animal was cleared to fly, to prove that they hadn't been exposed to it prior to vaccination - perhaps you could do something along those lines.

I got my answer from DEFRA, and though it wasn't what I was hoping it was what I expected: no exceptions, pets must have their rabies vaccinations in order to get in. 
Guess I will need to have a chat with my vet to see if we can come up with an alternative plan for combating the reaction or I'll have to forego my dream.