Just buy any MB and use these:
https://bitcointalk.org/index.php?topic=370907.0They are powered with either a SATA power plug or 4-pin floppy power plug,
have a built-in PCI-E presence mod for improved video card detection, are pluggable in any size PCI-E slot (1x, 16x, or any size in between), have extra caps for power filtering, and utilize a USB 3.0 cable as the means for transferring the PCI-E signals.
My understanding is that the board shorts these two pins already, so you don't need to run a wire. I got 5 working quite nicely, and 7 more waiting to be installed.
