Is it possible to configure the PCI Express lanes in a P67 motherboard to 8x/8x and use the second slot for a 4x SATA card (for example) instead of another graphics card?
I have never tried this, however I can't think of a reason this wouldn't work.
You should be able to put a single PCI Express x1, x2, x4, x8, or x16 card into a x16 PCI Express slot. The chipset should recognize that the card is not a video card and not enable SLI or Crossfire. If this isn't the case see if you can disable SLI and Crossfire within the BIOS.
Sorry I couldn't give you a definitive answer.