I believe the ECU delays the shutdown by 2 seconds automatically, provided that the failsafe signal is outside the taught range. In other words, teach the radio in the ECU with a given "shutdown" throttle position, but program the radio failsafe throttle position to a even lower value. This can be done by reducing the throttle channel to say 80% endpoint travel, do the ECU teach radio process. After that increase the throttle channel radio travel back to 100%, and set the throttle channel failsafe value to -100% (or whatever sign is low throttle). When done, set back the throttle channel endpoints to 80% and you are done.