
All you have to do is promise to be more green.
Missy is teaming up with the Sierra Club to offer the unreleased version of the track to anyone who signs the club's "2% Solutions Campaign" -- where you pledge to reduce your carbon emissions by 2% in 2009.
If you visit SierraClub.org, you can fill in the form to make the pledge, and presto, you've got access to the free song.