I seen that you found what you have been looking for, but here is my two cents on this anyhow.
I euthanize and freeze a lot of rodents. There are two ways to do it, first and the method I use is Co2. I use plastic tubs put the animals in it and run a line in to introduce the gas in. The animal falls asleep and the simply stops breathing. The second method is cervical dislocation (short and to the point, breaking their neck). This is easily done with mice by holding the mouse’s tail and placing an item such as a pencil on the back of the neck. Give a sharp tug at the tail and the deed is done. This method is not as pleasant to watch because of the twitching nerves. Both methods I've described are fast and clean.
Hope this helps.