I asked Merinta, maker of the Webplayer about using the USB for ethernet networking. Here's their response...
Being a customer of Virgin, you need to call them for support. But the
answer to this question is NO. You cannot use a USB Ethernet card with
webplayer at this time, because Virgin hasn't implemented the drivers for
any USB Ethernet card.
I would suggest that you contact Virgin with his request. And if Virgin gets
a lot of these may be they can implement this feature in the future.