You'll need the remains of a film pack to put the plate in. Remember that the film in the FPA bears on the inside of its front, not on the FPA. If you simply put the plate inside the FPA, it will be a little out of register with the GG.
I haven't looked inside an FPA for a while. You'll probably have to improvise something to hold the plate in position. IIRC, there are two springs inside the back of the FPA that bear on the film pack. I doubt they'll bear on the plate. I'm also not sure how you'll center the plate on the gate, but don't see why it can't be done.
If you can put up with the joy of loading the thing, I don't see why not.