xanaxez I see where you are coming from, but the term "humane" is a tricky one. In american society, that word comes in to play most often with treatment of livestock and pets. There are certain standards that have both legal and moral implications attributed to the word "humane".
These standards dictate socially and morally acceptable methods for killing livestock, putting down pets, and in the case of our hobby killing feeder mice(could be considered livestock I guess).
I'm not an expert on the subject by any means, but there are a few things you have to consider for any suggested method for "humanely" killing animals of any sort(this list is probably not comprehensive, and covers everything from ethics to practicality):
1) duration of the process. Quick is better than slow and drawn out.
2) amount of pain during the process. None or negligible is generally the acceptable amount. Generally, instant death is considered no or negligible pain experienced(it takes something like .75 seconds to register a traumatic painful occurance in the human body.. I forget the exact number)
3) ease of performing the process. If it's tricky, it is easy to screw up, and screwing it up usually results in what would be considered "inhumane" treatment by any prescribed standards.
4) cost of performing the process. This needs to be considered since we are all millionaires. It would be nice to say that cost isn't an issue, but it always is.
5) safety of performing the process. If you're risking your own safety with dangerous chemicals/equipment around, it's a bad method. If for some reason potentially dangerous items are necessary, then an extremely careful safety protocol should be followed.
6) scale of the procedure. Large scale operations obviously will function different than small scale operations. What is practical for 100+ cows a day is probably very impractical for a few litters of mice every few weeks.
7) mental anguish on the performer. Let's assume that bashing a mouse's skull in is an instantaneous and humane way to pre-kill(I'm not saying it is or it isn't, but let's assume that it is generally accepted as such). If you're going in to tears every time you do it so you can feed your snake, then this method is NOT one you should perform. Some will say that you should rethink owning a snake as well. This is something that should be considered when judging how humane a method of killing an animal is. I just imagine all the vets that put down terminally sick pets, they certainly have depressing jobs as it is and I'm glad they have better ways that smacking someone's pet dog with a heavy blunt object.