As for the rabbits - at least if you have no other choice than to feed live it would be a much better death than being put in a plastic bag that gets thrown against a wall, nothing deserves to die like that. I hated feeding live because it would take one of my snakes a long time to kill his rats, but I live where I can get frozen rodents shipped so that is not an issue for me. The CO2 chamber would be your best bet, I have never used one or know anything about them but it looks like some links were posted for you so you can see how to make one. Good luck, and I'm glad to hear you were thinking of the rabbits and you didn't want to see them suffer.