If you shoot 35mm film in a medium format camera, you're using film that's smaller than the image circle cast by the lens. Therefore, every bit of film is exposed, and the sprocket holes show up after processing. The problem is, using the film holder for my Canoscan 8400F scanner is no good, because it blocks the sprocket holes. Where's the fun in that?
I just placed the negative directly on the scanner's glass under the transparency backlight to get these scans. I didn't care if it wasn't perfectly flat on there because I shot it through a Holga to begin with. I've heard of folks flattening it on the platen using a piece of glass, too, to varying degrees of success.
As for modifying a camera to perform this experiment, nothing beats the flexibility of a Holga. Many others have done this before me, and I more or less followed the instructions at Squarefrog. An unused kitchen sponge worked great to keep the 35mm canister in place, and I did opt for the rubber bands on the 120 takeup reel to keep the 35mm film from straying to the edges.
So I have to wonder why anyone would buy a 35mm Holga...just buy the normal one and you get the 35mm version free.
Wind a few less clicks on the film reel, and the frames overlap, giving you a panorama, Holga-style.
I imagine this could work in many medium-format cameras, and I like the effect, so if I get my hands on one I'll be sure to try it.