Also, send an email to the buyer linking to a separate download location where you can download the tracks with license and all that crap. People can download it from this place if they want to hear it outside the Guild Wars game.

EDIT: One more thing, add a "use directsong" checkbox to the sound options tab. If you get tired of hearing the bonus tracks you can simply uncheck the box and listen to the original music.
EDIT 2: Yet another thing, please don't respond with "just turn down the volume and use WinAmp". Yes we know we can do that, this is simply for people who want to listen to Guild Wars music.