Beaglebone > cat5 > powerline ethernet adapter > single pair wire > powerline ethernet adapter > cat5 > USB-ethernet adapter > USB > laptop
Easy, right? I'm only getting a few milliseconds latency, so it seems to be working just fine. The black box contains the USB-ethernet adapter and a powerline adapter that is powered from a 3.3V USB power supply. Both USB devices are powered from the same cable. Now all I have to do is see if I have any problems when it's stretched out to 500'.