How to implement crow brake

Good afternoon, I’ve read and tried configuring the crow brake as described here: Differential Spoilers & Full House Wing — Plane documentation without success. I’d like the flaps to function normally with one switch and three positions, and with another switch to activate the crow brake only when the flaps are fully extended. My configuration is one servo and one radio channel for each control surface. Is this possible? Could you please explain how?
Thanks