It turns out that Apple's system for disabling the plugin uses a blacklist of disallowed iTunes additions in the iTunes binary. If you open the binary in a hexadecimal editor, like HexEdit, you can find the area where Apple has inserted the string "iPod Download" in its blacklist and simply replace the text with something else (in fact, I think you could probably just change one character) and your iTunes's original functionality will be restored.
(Thanks, Laurent, Rob, and Brent!)
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.