That behavior is not directly supported by the FailSafes as described in the linked documentation.
However, here is a workaround that might suit you: Configure your Transmitter with a throttle shut-off switch, which drives your throttle PWM signal BELOW 0% throttle. Thus when you flip that TX switch, the TX sends a throttle value below 0%, and trigger's the Throttle Failsafe as configured in ArduPlane.
(For example: My 0% throttle is around PWM 1100. I set my throttle FailSafe parameter at 975, and have my shut-off switch send ~950 corresponding to less than 0% throttle. This activates my Throttle FailSafe behavior.)