As everyone has stressed, make sure the husbandry is correct. The key to getting him to eat is making sure he is feeling completely secure and comfortable. With a snake that old, that has been so sorely neglected, I would get his enclosure set up just so (and in a very low-traffic place) and just leave him completely alone for 2-3 weeks, except for providing fresh water and making sure he's healthy. (No signs of mites or illness)

After he's had a nice long time to settle in, I would place a pre-killed rat in his enclosure and then leave him alone with it overnight. He may or may not eat it. Just remove it if he doesn't...wait another 10 days or so, and try again the same way. Eventually, he should relax enough to realize he is hungry and feel secure enough to risk eating.

I think it's when WE, as keepers, freak out about them not eating, and start trying all these different "tricks" every few days to "make" them eat, that we end up making the situation worse. Not that many of the tricks don't work...but I think a patient routine may be healthier and easier in the long run.

((DISCLAIMER: The mentioned method is currently being tried with a reluctant gopher snake, but has not been applied by me to a ball python. I am only speaking from logical thought, not personal experience.))