The closest anything has come using the Sandisk firmware is video4fuze. video4fuze makes .pla playlists from files added in MSC. It works on the Fuze and Clip+. I don’t know if it works with the Clip Zip. The combined lists it makes usually don’t last through the database refresh so I didn’t see any reason to try it.
It’s possible because Rockboxed Sansas use combined .m3u playlists.
