I'm thinking of a simple search box with a label "Type the song/artist you want to hear". Then, have it go out and search the Pirate Bay or some other torrent site and present a list of options. Basically I'd have it download the torrent for each search result (perhaps only highly seeded ones) and actually search the file list in the torrent, and present those to the user.
Then, when the user selects one, present a progress part and start torrenting. You probably would want to stick with highly seeded songs since the user won't have a bittorrent port forwarded to their PC. Or could you perhaps use the current transient outgoing port? I dunno.
But then once it's downloaded, play it---and provide a Save button.
They won't even know they're pirating.
Think of the glorious confusion it could cause if it got into widespread use! The RIAA would have to put out nonsensical sounding press releases like "that little play-a-song window that comes up on a lot of websites is illegal!" which nobody would understand.