I don't know if what I have achieved counts as successful, but I think I've got closest to working 12 bit on the 5D2. As we all know raw_rec produces split frames all the time, and I haven't had any success with it, but mlv_rec produces no split frames and only a small bar of noise at the top in 12 bit, or a large one in 10 bit, so I tried to move it down using digital dolly, and it actually got rid of the bar of noise! Clean, 12 bit, 1856x1044, continuous... AND MLV... on the 5D2... with potential to have audio!!! but of course tilt shifted down.
Proof:
If mlv_rec has something that is more functional it could be transferred to raw_rec right? Also there must be a work around to get it in the middle, maybe by adding blank space at the top of the video and making it so that digital dollying all the way down is now the middle? I'm sure this is progress, isn't it?