It is quite simple to substitute a SPDT on-off-on momentary miniature toggle switch (plus a red/green bipolar LED with current-limiting diode) for the OEM Fastrack controller:
Black to the center post, red and green to the outside posts, yellow to one LED lead and a 470 ohm resistor between the center post and the other LED lead.
Then install that in your control panel:
"U" is for remote uncouplers and "S" is for Fastrack track switch control. The unmarked toggles control my car-stoppers: