I thought of using a section of backing paper behind the film but wondered if it would scratch the film during transport? I guess it will be easy enough to try it and see...
I want to try cutting the ends off a 126 cartridge, feeding the film through the center section with 35mm cans as feeder and take up reels. Thinking that the focal plane will be more stable. I don't know if there's room on the feeder side for a 35mm canister. Will try tonight.
My newly arrived Kodak 104 Instamatic does not accept the trick of holding down the shutter while advancing the film. I think perforated 35mm film is out for that particular camera. Non-perf wouldn't work either because something will have to trigger the shutter lock.