If you remove the frets, then that solves the intonation issue that repositioning the bridge would cause on a fretted bass. You'd still have holes in the body from the original bridge though, and the pickup spacing would change. You'd also need to deal with the tailpiece.Could it be modded to move the bridge closer to the edge to increase the scale length?
then just remove the frets and have a nice semi-hollow fretless.
I've never tried this sort of mod, but it sounds like the sort of thing that would cause more problems than it's trying to solve.