Okay then here's your deal. You need two ethernet cables running to the wireless router, right, but there's only one cat-5 cable running through the wall to the upstairs area where you want to place it. Right?

Well, there's an old trick. Cat-5 cables, provided they're wired correctly, are eight conductors, only four of which are used for ethernet. I've successfully used ethernet splitters (one splitter must be used on each end of the cable run) to make one cat-5 cable in the wall carry two separate ethernet runs. This is a perfect application for that.

Edit: I notice Bitt already said that up above.