Swattiger: No answer on how to get the gas out just a note to be careful!! I had a broken pin on a can and when I tried to fix it I ended up jamming it in and the gas started coming out. I put the can in a bathroom sink and when I came back a few hours later the empty can was frozen solid with frost all over it. I'd suggest just writing off the can and researching how to dispose of it safely.
Lurkingnight: The only two gases i'm aware of as a lower power / less flammable alternative to green gas is HFC134a and HFC152a. 152a works in some guns but eats through the seals in others. HFC134a seems to work in all my gas guns without any problem. I've successfully used 152a in a Marui G17 and a WE Makarov with stock seals, and a DBoys Kar98K with all the seals in the bolt upgraded to Viton seals.