I'll be the first to say that guitar through bass amp doesn't sound great at all. I've played my Gretsch Pro Jet through an LM-II I used to own (using bass speakers) and it just sounded like mud. IMHO You'd be better off getting a guitar cab and waiting on the EHX 44 Magnum, buying some other cheap solid-state amp, or borrowing a real guitar amp from a friend/the lead guitarist.
However, I will say that you shouldn't need a rhythm guitarist if you just play more notes on bass and switch on a distortion.
