Steve strikes me as many things, but a creature of the night isn't exactly one of them. Although I admit he seems to be sucking the bottle-people dry.
Still, most of the weirdness of QC seems to stem from technology we could have, but don't. So we need to think of something along those lines to channel Steve down. What could be done? Hmm. Laser installed, done, on Pintsize; romance with machine, done (more or less), with Hanners; trouble with government, internet romance, gluing pubes to one's head, creepy alternate sex fetish, cosplay, furniture modification, all done, by Pintsize. The little freak guy has covered a lot of territory, hasn't he? Stalked by techno-crazy, done, by Sven and Steve; become super-hero, possibly done by Penelope and/or Sara.
Now we're moving to lifestyles. Hmm, family members come out of closet, done, by Faye; adventures in sex trade, done, by Veronica; mental illness, done, and done, and done; hobo, done, by Benji; alcoholism, perhaps done by Faye, and Steve's workin' on it now. Sex change? As bad as Steve's track record is with women, I'm not sure being one would improve him any.
So maybe we are left with the supernatural. Got it: what if Steve dies of alcohol poisoning and then takes up haunting Marten because Marten never told him, 'Hey, alky, get some help"?