I got my hand on this request. I just finished a new version of my Tools4Roku, which now allows you to rate the songs via the remote control.
You need perl and sqlite to use the tools4 roku. Maybe it can be adapted to WMP libary, too.
It uses the Left and right button, that are not assigned to any function during playback. So press right if you like a song, left if you do not like it. The new rating is then written into the firefly database.
Finally I can use smart playlists with the rating feature
I will do some testing and debugging at the weekend. So the next release will be out in one or two days.