i recommend using a functioning 34 bass with angled headstock and no fret inlays on the fingerboard. (epi toby, ibanez eda, curbow, squire deluxe J, etc... - well the squire does not have an angled headstock - but a stringtree can fix that).
just pull the nut and cut the 'new nut' out of the 1st fret fingerboard area - now the 1st fret is your zerofret. adjust sidedots to taste... voila a medium scale...
now watch your guitarist trying to figure out what note your fretting...
