Netduino Plus 2 use built-in usb for communication
Onboard USB is used to connect to the debugger. I recommend not giving up debugger functionality - you will need it. 

There is a number of .net Micro compatible boards with two USB connections. 

Have a look at STM32F4Discovery on which .net micro also runs. It has two USB Client connectors, one of which can be used to communicate with the computer. It is also very nicely priced. 

You may want to look into FEZ Cerbuino bee, which is Arduino compatible, which has an extra USB Host adapter. But I do not know if you can use that to connect to the computer.