I've done vocals with a fuzz box, flangers, compressors, mic into guitar amp re-mic'ed - all sorts of guitar gear. It won't neccessarily be HIFI, but sometimes that's not the point.
Try some of your guitarists stuff and see if any of that gets you going. Of course (s)he'll probaly make you get your own.
Depending on your mixer, you might also try overdriving the mic pres (turn them up till they clip) and experimnet with some radical EQ. Just keep the fader down low until you get it sorted out so you don't blow a speaker.
