I don't know if this will help, but I think you have taken the first big step of wanting.

Next, why does everything have to be perfection right away. Why can't you first get use to the situation first before going more extreme.

If i was going to learn something new, (non sexual activity) I would start slow and with steps. example: learning to ride a bike.

Get use to the different feeling, smells, and taste slowly.
Why don't you give him a hand job, but have your face real close and maybe even kiss it. When he cums, get use to the smell. It will probably still make you gag, but with time it should be less. Make it a game and if he knows what your working for, I don't think he would mind. I know that I wouldn't.

I saw a thread of a guy that said that it took him a long time to get use to the smell and taste of his women, but he knew that is what he wanted to do for her because she loved it. And within time the smell and taste never again became the issue to him.

Good Luck