Could I get some advice on selling music on a WP site, but letting people listen to it live free?

a friend of mine wants to sell some of his music on his current wp website, he doesnt want to only use itunes as the way to sell it because they take 40% like they think they helped write the damn thing :-p

thing is, itunes provides this SWF embedded file that lets users listen to the play list free, and if they want to download it to their computer then it costs money.

id like to maintain that feature, allowing people to listen, but not download, unless they pay through marketpress. any ideas?

Thank you