Sharing a Bluetooth Keyboard and Mouse sequentially between two Macs
I, too, was looking for an answer to this very question. Here is the solution that I came up with:


Go to System Preferences -> Bluetooth
Click 'Advanced'
Make sure that 'Allow Bluetooth devices to wake this computer' is
unchecked
Click 'OK'


Now, when I want to switch from my main computer to my MacBook Pro, I put the main computer to sleep and wake up the second one. The bluetooth keyboard and mouse both switch over to the laptop and away I go. When I want to return to the main computer, I put the laptop to sleep and wake the Mac Mini using its power button.