Foschi, I'm sorry, but all indicators are that the last thing to shut down due to cold in a reptile is the brain. There is no evidence that they're insensate or incapable of feeling pain simply because they were refrigerated first. Cold reptiles actually show the ability to respond, albeit slowly. Test this next time--take the refrigerated animal, and pinch its tail--I bet you will see it flinch in response, even if it's greatly delayed.
There is no way to make freezing humane for reptiles.
Remember, reptiles do NOT hibernate. They brumate. Brumation is a slowing of the metabolism while the animals is CONSCIOUS. They do not go to sleep and stay asleep.