Not to jack this thread, or sidetrack it... but if you didn't want to go the relay route and had a self powered usb hub:
Based on the pinouts found at this page http://www.taltech.com/support/pins2.html
Could you clip the pin 1 on your hubs, Type B port as shown in the picture (I know its very blurry but take my word for it, its the right pin).
My thinking is that if its not taking the +5v from the USB bus it has to take it from the Power Plug... this way I dont have to mod the motherbooard-to-usb connection, the opus power supply or the usb cable and I dont have to use relays. All I will have to do is take 5V from the molex to a barrel plug and put it into the DC power of the hub.
Would this work? Or would the usb hub not even work without that pin connected?