Having messed around with my own creations for shooting 35mm in 120 cameras, I finally bought these little jobbies from ebay. They work really well and enable changing rolls in daylight.
This first test roll was shot in a mamiya 645 and 35mm lens, using sprocketless 35mm from an old traffic camera. I used a 120 magazine which unfortunately left huge gaps between frames, but I think this will not happen with a 220 back.
Look left, look right