Clever? Yes. Unique? No. Spotify have "libspotify" [1] which allows developers to do pretty much anything (you could create a completely functional Spotify client yourself, which has actually been done [2]), but users can only use your application if they have a premium account.

[1] http://developer.spotify.com/en/libspotify/overview/

[2] http://spotyxbmc.tumblr.com/