Sometimes if I squeeze the thawed rat until blood drips out of its nose and then try to feed the snake it seems to make them more likely to feed, the scent of the blood makes them just a little more interested in the rodent...
Also I recently had my male Ball Python go off food and he just paced for about 2 and half months straight, I am almost positive he thinks it was time to breed and this is why he was pacing, I waited until he seemed to lose weight and then resorted to feeding a live rat, he immediately took it and then started feeding on his normal frozen thawed rodents after that.