The big problem with this is that each USB mic is digitised on its own with no reference to any other source of sync - that's what USB normally does. And the problem with this is that you can only have one source of digital sync into any DAW. What you'd need would be a means of taking several out-of-sync sources, and synchronising them within your PC. Now, amazingly enough, there's provision within the latest version of the USB spec for this to happen - you could, using the right mode, get all of your USB mics synced - Atmel can do this in one of their AVR processors. You need this absolutely, otherwise you'd get loud clicks and pops even when they're running at the same rate if the clocks aren't actually physically locked.
Slight snag though. There's not a manufacturer around who's done it, to the best of my knowledge - there's really very little call for it at all, and it would cost them a significant amount more to implement on what's seen as a cheap interconnection solution. So I'm afraid you're out of luck with this one.