I've made a few fretless guitars the conventional way (heh heh) and the lack of sustain on the unwound strings is a real problem for me (why so many people resort to a sustainer pickup). One of them was a solid maple-bodied Aria Pro II, so there's not too much more you can do with the body unless you build a granite one or something... heh heh. I would really like to build a FIVE-string fretless some day, on a six-sting platform. You could use all wound strings on a five, .022" - .070" or so. If you've played fretless bass much, you know that the way to play certain chords accurately is with two fingertips side-by-side, so the extra width between strings would be a help.
The five-sting bridge would have to be curved to accommodate the radius, but not intonated - a piece of brass bar would do. I have read that auto glass shops can cut and bend you a glass fretboard pretty easily and not too expensive, because cutting and bending glass is what they do...
So many projects, so little time & money. Venture capitalists, plz apply.... :cool01: