Hopefully some one will reply with a better method, but I use a tool called Advance IP Scanner when I lose systems on my network.
It finds the system name, IP and MAC address of the systems on the portion of the network being scanned.
With a little reasoning, you should be able to determine a pattern in the MAC address and figure out which board is which.
I have managed to do this with Symantec Ghost, as I completely forgot it has a built-in Inventory feature to record all hardware details of each machine.
which I have used and successfully found all the motherboards.