Best bet is to get a wall wart to power the TIU through the AUX port. Any 12-18 volt AC or DC adapter will do. Radio Shack has one; I do not have the model number handy.
Or, you could connect transformer to VAR IN, track to VAR OUT, and run a jumper between VAR IN & FIXED 1 IN.
If you ever start using 2 channels on your TIU, the wall wart is the way to go, to prevent losing control is a breaker or fuse powering FIXED 1 should open.