I've seen a few posts on this that date back over the years and would like to reiterate, because I can't believe that this problem hasn't been solved:
Why isn't it possible to route ringtones to earbuds? Or if it is, how can it be done? As BBs are being used more and more as music-playing devices, it's hard to believe that RIM hasn't solved this problem - particularly because it seems like it ought to be so simple to implement.