I'd probably get a cheap bass, but...
I actually played bass for a set on my guitar once when the bass player was late.
At the time I was using an octave divider that adds a synth note 1 octave lower that the note being played. I just turned the mix control totally to the effect...instant bass...if a bit rubbery. I wouldn't want to do it regularly, but it worked in a pinch.
See, I didn't reconize ya when ya first drove up till ya stuck yer hand out and wove then I seen right off who ya was and knowd ya.