There's been an article posted a few times that was written by Jason K., maybe? I'm afraid to even try spelling the last name knowing that I will totally butcher it.
He does say that a freshly cleaned environment can help. My guess is that a clean enclosure may sort of intensify the scent of the prey and thus trigger a feeding response since the snake's brain does not have to filter out the odors of the waste, sheds, and what not that the snake has been living with.