潘明丰 designed an awesome Hasselblad Back for Instax mini. Check the video out!
It does not require you to salvage an existing Instax Camera, it's completely mechanical, no battery. The awesome part about it its available to download and print yourself. Beware, it might be a bit tricky to build it if you don't speak any chinese. I didn't build it, so I can't tell for sure.
Download the files here, Password: 233333
If this link does not work, just ask in a YouTube comment for a new one, he's super nice and helpful! Or if you don't have a QQ/WeChat account, I can send you a download link as well.
If you don't own a Hasselblad like me, this project is about modifying it for a Mamiya RB67(which I also don't own). The cool thing about this is Dora Goodman designed the Goodman Zone, a DIY medium format camera accepting a Mamiya RB67 back. The Zone uses Mamiya Universal lenses, but you can make it work with any vintage lens with an included shutter if you know your way around CAD.
I did not do any work yet, everything published so far is from 潘明丰 and Dora.