To unlock the track "Through the Fire and Flames", beat the game.

In the Through The Fire And Flames introduction, before you start wrap a rubber band around Green. By doing this, you will not have to worry about holding Green; it does it for you. Make sure you press the other buttons quickly so that Green can register. If you hold the buttons as you do the hammer-ons, Green will not register, and you will fail.

Alternately, defeat Lou to automatically unlock the "Through The Fire And Flames" song for free.