I have only just joined the forum - my first kit arrives in August - so, it might be a little premature for me to start suggesting kits but would a touch guitar-style kit be feasible or even a Chapman Stick-type instrument? I know Krappy Guitars in the US give them a crack - custom not kits.
Also, I'd add my voice to a Bass VI. One of my regrets is not picking up an Ibanez SRC6 - their more modern take on the VI. (More generally, is it possible to customise any of the available kits to a baritone?)