If the mobo isn't specifically designed to support hybrid graphics (like some laptops do) you can't do as you proposed. Simply plugging in the stand-alone video card usually disables the on-board/integrated video adapter.
A sale representative from Lucidlogix told me that its working ...
"It will power down the GPUs and only use the Z68 if you wish."
From multiple reviews on the internet, it doesnt seem to work at all.
Maybe an upcoming patch will resolve this.
There's two modes 'I-mode a/k/a iGPU Mode' and 'D-mode a/k/a dGPU Mode' the salesman is correct if you're running in iGPU Mode. However, Virtu will need to have the game(s) profile in its' control panel. Then there's the performance differences with iGPU vs dGPU. nVidia is working on a 'better' solution for their GPU's...
Yes but as you can see, with the tested video card, power saving functions does not work either in I mode or D mode.
From all I have read, results have been mixed at best. Hybrid graphics seems to work ok with some notebook rigs, but desktop rigs have had less success because of all of the variables involved with different drivers and GPU chipsets. Good luck!