If this is what you do YOU HAVE NO BUSINESS feeding live.
Whether or not you like rodent, they deserve respect and not to be abused or tormented prior to death (what you describe is part of why snake keeper have a bad rep)
Additionally by doing this you are putting your animal at greater risk than if you were feeding live the way you should feed live. A mouse a a rat that would come out of it would become more aggressive than one that was not stunned.
The key to feed live is to have feeders that are well fed and well hydrated before being fed off, that is something YOU do while pre-scenting the room. Other important factor is feeding the right size.
After an hour of being in the same room simply drop the feeder in the enclosure leave it 10 mins and remove if un-eaten.
I have fed well over 50000 live preys and never stunned any of them and never had any incident and for animals that require anything larger than a medium rat I suggest feeding pre-killed or F/T