I am working on this myself. Although I raise mine for meat, I nonetheless want to make the kill as quick and humane as possible.
Great to see someone show compassion about the animal when it comes to dispatch. I was on the eat birds forum and I confronted someone who slits the throat without stunning,which I feel is one of the most barbaric things you can do to an animal.
I have tried chopping (very hard with a big turkey with a thick neck), then stunning followed by slitting (one turkey woke up during the bleed out even though I whacked her twice with a steel pipe, so I won't be doing that again). I would never use ether because then you are just suffocating him. Easier for the killer but not the killee.
I have come to the conclusion that my method of choice will be stunning (again with an iron pipe), then a quick decapitation with a sharp knife so it will be dead before it can wake up.
A 22 to the head would be about the quickest method, though. For those of us who raise them for meat, that wouldn't be very practical in the long term but could certainly work in your situation.
Good luck, and I admire your choice. Even though I don't see mine in that way, it is always hard to put down a pet.