This idea here is slicker than dog snot!!!! http://makezine.com/2015/02/05/blizzard-hacks-build-a-clever-avalanche-roof-rake/
A little too aggressive with that would likely do more damage than pulling. As long as you don't try to get the last inch either should work. Pushing up I'd rather have wheels to keep the cutting edge from snagging the shingles though.