That Might Work
I own the Apple wireless keyboard. As far as I can tell, it is only a BT input device. But, here's the deal:
The pairing function might require you to only use the keyboard with one computer at once. I have my everyday OS X partition and then a "virgin" OS X partition with Disk Warrior. I was able to pair the keyboard and mouse to both systems.
BUT, If I start up my PowerBook from the second partition through FireWire target mode, I cannot use the keyboard to run both computers. The ironic part is that the keyboard cannot wake a computer from sleep. So, if you are using it with the Mac, put the Mac to sleep, then pair it to the PC. When you are ready to use the Mac again, just wake it from sleep and it will pair again. I know that works because I can use the keyboard on both my Macs, as long as one is sleeping. I don't know how easy it is to pair a keyboard to a PC, but is bloody simple on the Mac. You might be on to something, give it a go.