the nearest there is which blocks playback of 'flagged' songs is
http://nunzioweb.com/daz/plexcluder.html but that essentially works via the playlist editor and there's no means to set a button into the Winamp ui to enable it but can be done via drag+drop onto the window or via the playlist editor menu or using alt+x (though i probably should at some point add support for a 'sendto' menu item to do it which covers off library usage).
-daz