I'm pretty weak on my effects knowledge, so maybe it can work, but whenever I ran my guitar through an octave-down because I wanted a Bass VI, it sounded like a muffled, distant, kinda fuzzy version of the notes. When I would try a pitch-shifter to turn my guitar into a baritone, it sounded like I was playing music for a 1950s underwater movie scene. Neither one of them sounded anything like the instruments I was trying to emulate.
Maybe there are ways, I couldn't figure it out. By all means, give it a shot [and let me know if it works!] but maybe try it with a demo in-store before buying the pedal; you may find that you're better off keeping that money towards an actual Bass VI.