I have an auto-load/rewind P&S that I needed to pull the film from before shooting the whole roll. It was a bit complicated but it worked.
First I shot one last throwaway shot and took out the battery.
Then went into a pitch black room with the camera, an old opened canister and reel and a piece of masking tape (oh, and a scissors). In there, I opened the camera, pulled a little bit more film and cut the film about 3/8" from its canister.
I then taped the tail of the exposed film to the old reel, put that in the old canister and squeezed the cap on as best I could. I put that canister back in the slot and closed the camera.
After all that I put the battery back in the camera and let it rewind the film. I took out the film and squeezed the caps on a little tighter with a pliers.
I pulled a bit of film from the original roll, cut the tail to look like a new one and put the rest back in the camera.
In the end I had only lost about one picture from the first set.
All this is easier to do than explain.