I'm not sure how possible this is. Aside from the basic trouble of remapping, how is your computer to tell the signal from one keyboard from the other? But I'll let the more technically minded handle that part.

My solution for the "I'm too cheap to buy an X-Keys (despite my ridiculously expensive computer and nearly 40 bucks on month on WoW) problem" was to get a USB Numberpad. They make them mostly for laptops. It's simply a stand alone numberpad. Which is nice for keybindings since numpad numbers are counted as different strokes than the top row numbers that most people already have spells bound to. It's not programmable in any way, so you'll have to work your keybindings to match the lay out, but it is a handy extra bunch of buttons. Maybe less useful if you're already using a keyboard, but if you are using a gamepad (like my Nostromo) then it's pretty handy.

But make sure to check the cable size. Since they're mostly made for laptops the cheap one I bought (which is pretty nice actually) only has like 2 feet of cord. So I had to rewire my desk a little and just moved my USB hub up a lot closer to where my keyboard tray is.