I would say you should definitely NOT chop his head off or use CO2. Snakes can live a long time without their heads (compared to mammals) and its a terrifying, hellish experience for them. The snake's metabolism is so slow that CO2 (or injected drugs for that matter) would just cause a very long, painful and scary passing. I'd say that a freezer is your best option. That way his brain will go into a dormant state before anything painful starts to happen in his body, it will also make the pain of the wound go away the fastest. (People have said that the ice crystals forming in his cells would be painful, but that just isn't true. A snake would be dead long before any area of its body got to 32 degrees.) I'm so sorry that you had to deal with this. Good luck :-(
