So not sure. I tried searching around for NEX and FullFrame but not seeing anyone asking specific questions on them. Are the lenses full manual? (I have never used NEX lenses on my FS100). If not, how will you control the Iris?
It won't work. Even if you were able to find a way to mount it on 5D, you will get massive "vignetting". A FF sensor on 5D is simply bigger than what NEX lens can cover.
The simple answer is no. The flange-focal distance on a 5d is MUCH longer than on a NEX, so the lens would simply be too far from the sensor to focus.
Theoretically I guess it would be possible to have an adapter with a lens which corrects for that, but I doubt whether anyone would make such a thing. If they did, then you could worry about vignetting....