I haven't been able to get this working with my Thrustmaster T300 RS - incase anyone is curious.
I had the gamepad plugged in and it picked that right up - so I closed the game, unplugged the gamepad and tried again. Nothing. So it might be hardcoded to Logitech G25/27 wheels.
I won't be buying a G29... ever, so I don't know if it supports that or not.