Apparently you just need M.2 to PCIe x4 adapter + PCIe x4 to x16 riser to get desktop video card(and separate power for the GPU oc) working on NUC.
pics: http://imgur.com/a/JHoIy
more info: http://hardforum.com/showthread.php?t=1865546
Dear Intel, please add mPCIe port on gen6 NUC models.