I hacked a LCD Loop/Hood - for my T3i. I bought a cheap ebay diopter eye cushion, just to have something that connected w/o tape/magnets, etc.

Drilled a couple of very small holes for the very small screws that hold the LCD hood to the diopter eye cushion and then put the two together (with a tiny piece of foam as the there is a slight angle to the LCD hood.)

Works wonderfully..... except. It is big, heats up a sensor that isn't designed to be "on" all the time (I imagine I could train myself to hit the live view button in the 5d3).

I did buy a LCD hood for the 5d3 just haven't gotten around to the other part of the hack w/ the eye piece.

With Magic Lantern I get all the focus/exposure features. Just in a large form vs. through viewfinder.