Unfortunately, I don't think that will work. I think Z68 is the only chipset that will allow you to have both a discrete GPU and Sandy Bridge's integrated GPU enabled. I don't know whether it allows you to have both working at the same time though.
If you actually need two PCIe x16 cards in those systems, you're hosed. There is no pass through -- you still need a second PCIe slot and neither one has two of them.