Currently you can +1 rate by pressing the lv button (which I cannot get to work on the 6d outside lv, though 1% says it should). Anyway:
Problem: You can only +1 rate, for decreasing the rating you have to +5 rate by clicking 5x. Plus moving the finger from the back dial/multicontroller left/right to the lv button takes a little time which does accumulate if rating 1000+ shots.
Suggestion: In addition to lv button, rate +1 with multicontroller UP, rate -1 with DOWN
Edit: ok, ok, I've done it myself :-p ... https://bitbucket.org/hudson/magic-lantern/pull-request/245/rating-use-up-down-for/diff