I do not speak from experience, but the idea of 'freezing' has always unsettled me. Is such a death quick and painless? (That's an honest question, not a rhetoric judgment.)
What about using the CO2 method used for killing rats? I would assume it would have the same effect on a snake, and from all accounts, it is the most humane way to do it; no pain or discomfort, just sleepiness and then bye-bye. Perhaps somebody with experience can chime in on that.
Regardless of how you do it, I am very sorry for you and the snake. It must be a very disheartening experience for you. Take care.
