"The longest wires would have to make the run all the way from your start location by the yard to the track on the opposite side of your center opening. "
Not really, he just needs to connect a pair of wires to the part of that track closest to the TIU, on both sides of the opening. The track will conduct the signal the rest of the way around. Those locations are just past the switch on either end of the layout that lead to the opening.
I would not wire DCS without using blocks.