Thunderbolt Displays' ethernet adapter breaks MacBook DHCP/MAC Address reservations
Solution 1:
This depends a lot on your DHCP server, but I would look into using the client id to assign static IPs. It's not tied to the individual hardware (although you'd have to set it at least once when they first use a TB Display), so it avoids the switching displays problem. It can be set via the networksetup tool.