It should be quite possible, with some tinkering, to get a usb-mini to RS232 cable going and to use that via Xterm. You could even use a bluetooth keyboard like a Thinkoutside foldable to make text entry quick and painless.

As far as I know every serious router and switch ever made can be controlled via a serial port console, and getting the 770 to talk over usb/serial should be doable.