You certainly can rethread aluminum (gee, think the guy at Ford wanted to sell you an oil pan?). I mean really, does that guy think the threads are cast in or something? They had to be tapped at some point.
Helicoil (oversized threaded insert) would work well, and you might be able to reuse your old drain plug. You basically drill and tap the hole larger and put the insert in. Some kits come with the tap you need as well, and you do it by hand.
I know the box of drain plugs at work contains some that are self-tapping for just this situation. Can't comment on how well they work, but they do exist.
