I believe that's what Jaco himself did, if I'm not mistaken. Rumor has it that he pulled the fretwire out from a normal J-bass and then spackled the slots with some kind of polymer cement or something. Also, my one friend, fellow bassist and astonishingly good (I've seen him make pros fight back bitter tears of inadequacy), told me he heard about guys doing that... popping out the fretwire and putting some kind of goop in and smoothing it out. Any truth to that? And ultimatel what is the proper way to defret an axe? I have this strange notion to get a double-humbucker MusicMan Stingray or Bongo and defret the thing. I don't know why... but it's in my head.