[PCI-E] Switch 8x to 16x?

I've read about SLI mobo's having each slot run at 8x but I was wondering if I could switch it to 16x until i get a second card?

Mobo: DFI nF4 SLI Infinity

btw my XFX 7800GT idles at 42C. good temp?

they run at 8x when two cards are inserted, and 16x with only one card.

well under the nvidia tab it shows:

Bus: PCI Express x8

you may need to go into the BIOS and set it to run in Single card mode.