The Cerb 40 uses the OSHW firmware. At the present time, the OSHW firmware does not provide USB client support for HID devices and CDC. This is only provided by GHI for devices which use the premium library.
The Micro Framework does provide a low level USB interface , so you I suppose you could implement a client device driver.
@ Gus - What would be the minimum number of Pandas? I’ve got a big box of eBlocks that I use for education, and could use some more pandas (and the eBlock shield design files) to increase my max class size.