I'll tell you, I've only removed a ding in my shaft once, but I used this method with very good results!
This method uses steam. Take a small pot of water and cover it with a doubled-over sheet of aluminum foil. Poke a pin hole through the top of the foil and boil the water. This should give you a relatively constant and focused stream of steam to use. Put your shaft a few inches over the hole, hitting the ding for five seconds at the most, then wiping off the surface moisture and checking the dent. Repeat until you get to the next part. When you feel the ding start to come up a bit, let it sit and the latent moisture will do the rest. Then treat the shaft using your favorite methods.