I've never tried this but it just occurred to me, instead of trying to make a 35mm cassette work in a medium format, why not wind 35mm bulk film onto a 120 spool?
Get a spool with a used backing from a normal 120 roll. In the dark room, stretch out the backing with the front side (black side) up, maybe use some pins or tape to hold it down. Turn the lights off and stretch film out over it, then tape or staple the film onto the end. Roll up the backing and film onto a spool as taught as you (reasonably) can. Use some tape to hold the roll together.
I would suggest either taping both ends to the backing or streching the film all the way to both ends. This way when you begin rolling the film onto the take up spool in the camera, the beginning of the film will guide correctly into the spool and not get loose and/or caught somewhere.
This would solve both the problem of a lack of paper backing for the pressure plate, and it would allow you to count and measure frames just like a normal roll of 120 would!
Alignment can be done with the paper backing as a reference as well.
Best Luck!