Would something with baking soda in it work? That might help neutralize the acid.

I used to use something called Gel Kam for a tooth sensitivity. It is fluoride and is supposed to help strengthen the enamel. It is an over-the-counter item, but usually you have to ask the pharmacist because it isn't always on the shelf. It is kind of expensive, so maybe you should ask if it would work for you before you try it.