Nuelectronics Ethernetshield and PoE

Hi there..
Just a small idea that came to my mind some time ago.. wouldnt it be possible to wire the (or any) Ethernet shield to Vin with the appropiate stuff (like 15-33kOhm resistor..) to use Power over Ethernet instead of a second source for power with those shields? It'be some nice modification i guess.. and i wonder if someone had done this already..