Check out allergichobbit on Youtube. I can't get it, due to dial-up connection, but I saw a little and hear it's great help. You gotta take it slow. don't try to take off more than a 1/16" bite or so. I think a lot of guys would be using a purcussion tool @ the start, a golf ball sized rock, sorta rounded. Get a pad for your seated thigh bone and support your glass against your leg w/ your left hand, protect your left hand too. The glass will break @ a 100 deg. angle from a 130 deg. blow.
how's that for confusing? Get you some superglue, duct/electrical tape and some bandaids out there too.
Check out the Youtube vids if possible, I think that will give you a good idea of what you're after. Good luck....and watch out that you don't get addicted.