I purchased a diamond python a couple of months ago and was guaranteed that it would only eat live food. So I let him stew over that for a month and then offered him a frozen one (thawed, of course). Of course, he happily ate it. I think the problem had been that the previous owner had been feeding him too often and he was just being fussy.
And like you Kiwicam I defrost mine in hot water. I used to put them in a bag but now I just throw the mice/rats into hot water (as hot as the tap allows) and they warm up in a matter of minutes. This still lets the mouse have a heat emission that will help with heat seeking pythons. Give some movement along with a heat signal and most pythons will be fine with it.
Of course, there is absolutely no issue with freshly killed either. So long as you regularly worm your snakes.