I'm certainly not the one to think this up, though I've tried similar with Polaroid film in the past without success. There is currently some activity in "reclaiming" a full color negative from Fuji FP-100C. There is a good thread on Filmwasters and they also cover it in a video podcast I believe, but I figure I would quickly go over the process here, as one can never have to many useful Internet resources!
First off, don't be put off thinking this is difficult. It took me awhile to get around to messing about with this, and it took me about five minutes to make my first color negative, plus drying and scanning time.
Basic supplies are bleach, a brush, some kind of surface such as glass or a piece of plastic, and water. Also, of course, the remains of a Fuji FP-100C...the back side that you would normally throw away (you'll see what I'm talking about in the step-by-step).
So you have your bleach and brush...
That's it! Makes me sad about all of the Fuji negs I've thrown away in the past, particularly from my Japan trip. There are other methods out there on the Interwebs. Some use paper towels or sponges, some use different chemicals. Experiment and see what works for you.
On a side note, I thought to try this with black and white film, to see if I could get something similar to Type 665. It works...sort of. I chose to use Fuji FP-100B, because the 3000B already has a scannable negative. And I figured it would be most similar to FP-100C. The big difference is that the image on 100B is on the developer, not the plastic, so it washes off, and washes off very easily. So...it is possible to remove the black backing from FP-100B, but you can't get any water on the other side. This is very difficult to accomplish when you are trying to rinse off the bleach and black coating. After a couple failed attempts, I chose to just use the paper as a handle and painted and rinsed very carefully.
A bit messy. The original print for comparison.
Here is another previous, mostly failed, attempt with FP-100B with much of the image washed and scratched off. This one I attempted to tape down to seal off the emulsion side. Print and negative...
And this does not work with Polaroid films, as the black backing doesn't dissolve from bleach.
I also wanted to try Type 689, as it seems similar to FP-100C, or an earlier version. Some people believe they are they same film, but this experiment kicks that idea out the door.
For some reason, I saved a bunch of Type 689 negatives (and other types). No idea why, but glad I did now!
So, to summarize, the following film types have been tested by me (or verified by others as with the Fuji 4x5) as working for negative retrieval (a few) or not working (most).
Working (backing removable with bleach with transparent negative)
Fuji FP-100C, FP-100C Silk and FP-100C45 (emulsion will discolor and deteriorate with extended exposure to bleach)
Fuji FP-100B and FP-100B45 (emulsion washes off if not very careful)
Polaroid Type 689 (very dense blue negative)
Not working (possible to remove black backing but emulsion is opaque)
Fuji FP-3000B (emulsion opaque, but already has a scannable negative image)
Type 667, 107 and 47 (emulsion opaque, but already has a scannable negative image)
Type 669 and 108 (can scrub back off but black underneath, emulsion opaque)
Type 690 (can scrub back off but black underneath, emulsion opaque)
ID-UV (can scrub back off but black underneath, emulsion opaque)
Chocolate and Blue 100 (can scrub back off but black underneath, emulsion opaque)
In closing, another reclaimed negative saved from last year...