I've been mooched off of plenty of times by people I like, but I've also done my share of mooching, so I can't really condemn them for it.
The easiest way out, and what I've done in the past, is to lie. Just tell them you also have no monies. A more stressful (but in the end better) way to solve the problem is to just explain that you're not their wallet and if they want to keep hanging out with you they'll have to pay their own way. I'm sure that in a group that size you'll find at least a few who are willing to change their habits and spend money on some pretty girls.