I happen to come across a solution for this today when looking for something else. If you are the valid license holder (i.e. you can play the song in iTunes) then this program can stream out the contents into an unprotected m4a file. It only takes a couple of seconds.

I'll wait for Tony to say whether I can post the link. In the meantime, I recommend dbPowerAmp for transcoding all formats. The forum at their site has lots of good information, too.