http://www.youtube.com/watch?v=2GVyaR1EaeY
Add a Roland Bass Cube and you are set to go. Sounds more like a real bass than any acoustic bass guitar, they all have to be amplified to be heard anyway, it cost about what a good set-up for an upright would cost (apparently), and it's dead easy for a guitarist to play. They've come out with a 25" scale length - basically the same as a guitar - but I like my 23" scale just fine: I like to play fretless and it falls under the fingers more easily.