Wouldn't it be more effective to add a FET switch between the buck converter and final load, to give total isolation from the feedback circuit and other leakage loads etc?
A static switch will need / waste less energy than driving another FET gate at high frequency.
You could add a diode and high impedance RC storage / discharge circuit to feed the switch FET gate, driven from an appropriate point on the converter, such as the upper gate driver for an N channel, or pulled down by the switch for a P channel.