It's simpler than you suspect. The design doesn't include a NAT ROUTER that would be required to use more than one such interface.
In closing, I'm sure you could plug it in, but it will not work. Let me share I will not detail why.
I have a simple DSL router that can connect to a pc via a Ethernet port or a USB port, obviously for machines that cannot support Ethernet. Just looking through the manual it repeatedly says you should not use both at the same time, but I have been using both so I can get two machines on the net, i.e 1 has the ethernet cable and the other has the USB, why is this not supposed to be allowed, both connections wor fine or will it cause a strain on the hardware?