Well I took your OP stating a "35mm digital back" as asking for a 35mm sensor but I see that could be interpreted in different ways. I still maintain that it is not possible to:
1) Put a digital sensor in the same space the film plane occupied on a existing film camera
2) Connect the analog controls of a film camera to a digital back
3) Include both the electronics and any meaningful size battery in the space currently occupied by the film canister.
Originally posted by Vicioustuna2012 I've actually been researching it a lot, and from what I've gathered, it's actually very possible to create such a device
Again please post a source, I am curious to see and read what made you think it could be done.