I found a way of gelock-like sync in liveviewmode with the 5dmk2. 
a short testfile:  -> http://www.goggi.de/5d-genlock-sync/-allPreview.mov

I also made a test with two 5Dmk2. a 3D shot over 7 minutes, both cameras in sync from start to the end.  -> http://www.goggi.de/5d-genlock-sync/450-seconds-3d-sync.mov


here are my 27 testtakes with a steppermotor, original 5dmk2-files, one after the other, all in sync. 

the 5Dmk2 movie files are quite big, 19MB each, please be patient, it will take sometime to download..

genlocks@goggi.de