You'll have safety Nazis come in but I've been running all year with just shorting the 2 pins on the cable, no add power adapter or anything. I was just using a paperclip at first but since every PSU is EVGA now I have tons of their "tester" adapters that short the 2 pins.
I'm not afraid to start a power supply by shorting the two pins together with a paper clip, done it before for testing. But what about the sequence of power being applied. The power supply will light up the graphics cards with the two 8 pin connectors and power would be supplied to the "risers", in this case additional PCIe connectors that connect to the motherboard. I'm kinda worried that 1/2 of the cards and part of the mb will receive power before the rest of the system.