How to play bass track with guitar ?

["Marc" <marc@clubcapelli.com>]

Hi,

On some loops, it can be cool to have a bass part with the drum on the 
back,
but switching from guitar to bass and return to guitar can be a little too
long on stage.
Did you have a solution to play a bass part with your guitar ?
(I've tried with my HOG, and with Octavers/Harmonizers, it is far from a
bass sound, even a synth bass sound...)
Roland VG ? 
Sound to midi interface like http://www.sonuus.com/ G2M, connected in midi
with a expander ?
All your knowledge is welcome.

Marc