I haven't tried this myself, so I can't say it's 100% true (or foolproof), but I've read that you can us EZ-OFF oven cleaner to remove the anodizing from aluminum. The guy that was saying this, said that you'd need to coat it heavy, and let it sit over night. Maybe spray some more on there from time to time. In fact, if you have a thin or small part, you can spray the ez-off in a bowl or pan until it builds up deep enough for the part to be submerged. That way you don't have to come back and spray it again.

I have used ez-off to remove paint - works like a charm on metal or plastic. I also got some dye out of a set of HPI wheels that I picked up in a trade. They were dyed pink, so I soaked 'em overnight in the ez-off and by morning they were almost white. Then I re-dyed them a color that I wanted.