If you cut down a GPU to only 64 "cores" and only 700 MHz it may very well consume only 5 W. e.g. AMD Brazos/Kabini.

Come on, are you being difficult on purpose? How are you going to boot the graphics card? Access network or disk resources?

I'm pretty sure the Adapteva chip can't do that either; it requires a host processor just like a GPU does.

... which is on the board.