Dave,
I have tears in my eyes as I type this. I have been through care for a cat with FIP. It was one of the most heartbreaking things I have ever been through with a critter. I know what you are going through. IF kitty starts showing signs of pain, please make sure it gets pain relief. This disease really sucks, and personally I would let the cat go before he suffers to much.
Little Joe, my friend's little guy, went downhill very rapidly. I was helping with his care. At one point, we had to force feed him, plus give sub-cutaneous fluids. After 2 days of that, it was too much. It was not fair for the cat, and too hard on us. He was put down shortly after that.
If you have other questions, please let me know. If you are still interested in alternative treatments, there is a vet is Sebastopol that does alternative and traditional care, including acupuncture for animals. I can get the address for you if you want.
Here's hoping it is not FIP. Sending healing thoughts to you and your little guy.
And thanks for rescuing a kitty like him. I'm allergic to cats, otherwise I would have a couple of them, all rescues.