Construct metal walls alongside the northern side of (022, 022) across to (024, 022), for a total of 42 WP, do the same across (026, 022) to (028, 022) for another 42 WP.
Install a metal door on the north side of (025, 022) to connect with the walls for 10 WP.
Install a switch on the south side of the metal wall on (026, 022) for 6 WP.
100 WP spent, none wasted.