I once modified the battery compartment of a Polaroid 104 camera, converting it to take AAA batteries. As far as I know it's not much different from the 100. Could you post some detailed pictures of yours?
I've done the same. Pretty easy, considering how I generally lack the skills for such tasks. It does sound like the original poster's problem may be a bit more tricky, though. Could you possibly post some photos around the corroded rivet area? If your soldering attempt did not work, my guess is that you may have to find a way around rivet, if possible.
"If it can be written or thought, it can be filmed." - Stanley Kubrick