Most people have been reporting that the slot is missing the Mini-PCI connector, so you'll have your work cut out if you want to use it, in theory it would be possible to solder your own connector in, but it's certainly not something I would attempt.
I believe the wireless card is in a Mini-PCI slot, so if you were willing to remove that you could put something else there.
The other option is just to use the space of the slot to house a USB device which you connect up internally.