Thanks for the responses. The more I thought about it yesterday and after fiddling with everything possible, it was painfully obvious that BT5 isn't going to recognize the Thunderbolt Ethernet controller. Sad, but to be expected I guess.
With VMs so commonplace now days, I never considered that it may have been wise to hold on to my ThinkPad. Oh well. Guess I'll keep using it via OS X and the 192.x.x. address and if necessary I guess I could try a USB->Ethernet adapter if I really feel I need to connect it to BT5.
Thx again.