[Porsche-O-Phile]

Public humiliation is a great weapon.

I'd circulate a public e-mail thanking all the attendees and special recognition to "Person A", "Person B", "Person C" (etc. - name all the paying individuals) for "...graciously stepping forward at the end of the night and offering to assist in helping to pay the tab". In this way, you don't name names of the leechers, but it's pretty obvious by omission and (hopefully) a few of them will be shamed into ponying up to the decent folks who stayed and paid.