Fastrack switches that are o-60 and larger already have "integrated" isolated sections on both the straight and diverging routes.
If your switches are smaller you can add an isolated section between the switch and the siding. simply remove the center wire to break the power connection.
These are the larger isolated sections, I believe many if not all of the smaller "fastrack fitter" pieces have the wires and rail breaks to isolate a track.
Run the power wire from your transformer to the input of a toggle, run another wire out of the toggel the the center rail of your siding, and viola!
There is no need to break the outer rails.
