I used the rubber grommet that the parking brake cable goes out through. Or is it for something else? Anyway, there is a large rubber grommet under the dash on the drivers side, below the master cylinder level. I made a small slit in the periphery of it and I have bunches of wires threaded through there.
The only wire you need to pass through there is one pair for the sensor. If you use a twisted pair in a "sheath", that's only one cable to pass through and it's very easy. I do hope you're not using the original harness that far down.