u guys also running 5 gpu?
The load on PSU has no bearing on the power switch. It simply grounds a signal line to tell the circuit to ground the PSU power-on pin (green line on ATX connector), which also has no load on it. This signals the PSU to switch on with it's own internal load bearing circuit.
So any NO (normally open) momentary switch will work (like the ones at Radio Shack or any other such place). Solder two wires to the switch and add a two-pin connector on the end. I just made a couple here a week ago for some boards I have open air. Touching a small screwdriver across the pins also works. Usually those pins are color-coded red on mainboards.