help with switch wiring

I'm not sure which section this should be in so mods, move if necessary. I'm going to be running dual PSU's in my new build. I know how to wire them both together so that they both turn on when the power button is pushed, but that's not what I want. I want a seperate toggle switch for the secondary PSU, I can do this also. The thing I don't quite understand is how to make sure that the main PSU(cpu, mb, etc) won't turn on unless the secondary PSU(WC, fans, etc) is turned on. I was thinking that if I took the green wire from the primary PSU and wired it into the same switch as the sec PSU then back to the 24 pin connector on the MB then the pri couldn't power on until the switch was flipped. I hope that makes sense. I need somones who knows more about this to shed some light on this for me. Thanks.