I'm not sure if the types of polls I've seen, on other forums, would work the same, here, but I imagine that a simple poll could easily be posted on the song download thread, itself.
It could look like this:
Rate This Song
On the other forums, the poll is set up to only allow each member a single vote and you can't see the votes until you cast your own (which would address the issue of being influenced by how other people have voted).
Of course, it would be up to the artist whether or not (and which tunes) he wants to do this with. Plus, a separate thread could be started, elsewhere, where the artist can enter the song(s) with the highest ratings into a "Best Of Genre" type of poll/contest (like the SOTM and SOTY ideas that have been bouncing around).
This way, it would be up to the individual and not require the staff to get too involved.
...just a thought...