Apple Bluetooth Keyboards and Mice
I don't know of a way to make it only pair with a single KB/M/Trackpad, so a workaround it to prevent it pairing with anything further once you have paired what you need.

One method to do this, on the assumption that the users of the computers do not have administrator access:

Step one - turn on parental controls for the users of the systems in System Preferences &gt; Parental Controls:



Then turn on Limit Applications, and scroll down to untick System Preferences under Allowed Apps &gt; Other Apps



Now make sure that the Bluetooth menu bar item isn't shown in System Preferences &gt; Bluetooth:



Obviously this may prevent legitimate access to other system preference items, but as I cannot find a way to lock down Bluetooth to Admin access only, then the next best thing is to prevent you from getting to the Bluetooth config areas.  It may still be possible to manually start the Bluetooth assistant, perhaps someone could comment on that.