What's this about Yosemite only supporting TDM over Thunderbolt? I just used TDM via the FW400 port on my mid-2009 Macbook(running Yosemite) yesterday. I've also used that same computer with many other computers that were operating in TDM, and it mounts and reads the drive fine-just as if they were an external Firewire HDD.
TDM is operated by the low-level operations of the system(EFI in Intel Macs, Open Firmware in PowerPC Macs), and the OS really isn't involved.
With that said, with the computer only having USB in and out, I'm not sure how TDM would work. I don't think, for example, that it's available on both the Aluminum Unibody Macbook and on the later Polycarbonate Unibody Macbooks, as these both only have USB.