I've heard of doing them with one of those balls, swiss balls or whatever, heals against the wall, knees in the balls or something but never have tried it. Think it was Mike Miller from Nazareth Barbell, can look at Nazbar.com they have a new discussion board and are pretty good at updating stuff.
I've never tried it though, I look geeky enough without rolling of a ball near all the ab-people.
I do 45 degree raises, pull throughs, romanian deadlifts but without a real GHR it just ain't the same, IMO!!!