That was going to be my suggestion too. It's a bit of a pain, but it might actually work in this case.

We had to feed our last cats in separate areas of the house (not because of food bullying, exactly, but because they just didn't get along) and it worked pretty well - especially after we moved into this house and were able to feed them on separate floors. We did generally give the less aggressive cat her food near where we spent most of our time so that we could keep an eye out for the other one trying to sneak in and eat it.

I must say that even after all these years, it still hits me how wonderful it is to have cats who get along as our two current ones do.