As far as I know this is not impossible.
I think you could benefit from reading hessi's "using itunes" series; I'm gonna give you a relevant quote from him:
Unfortunately, I have not yet found a way to keep these songs out of normal rating-based playlists, which means that tracks that are not rated yet could show up in your 5 stars playlists just because you rated the album with 5 stars. My advise would be to stick to one logic, either rating tracks or albums, but not both.
http://hessi.tumblr.com/post/1116843969/using-itunes-part-4-lets-get-the-rating-started