Ok, well for while I have had this idea. Call me crazy if you want, but I think it will work. I have yet to try it with unexposed film.
I found an old Polaroid for illustrative purposes;
As you can see, the Polaroid type 600 fits into the 4x5 holder quite well; it's thin enough to go under the rail, but stiff enough not to flop around..
I have an old Polaroid Land OneStep. It looks like the front door that contains the rollers could easily be taken off in one piece. There is a large gear to the side, which I can spin to turn the rollers, and drag the film through.
So, theoretically, I can shoot the film in the 4x5 holder, then run it through the rollers in the black bag, and voila!
Does this sound plausible to you? It would require the breaking of a film pack, I don't know how hard that is. Does Fuji make an equivalent that would function in a similar way?