You can either use another joystick or knob, and mark the spots you need to hit to achieve the right setting as if it was a 3 position switch.
One of the robot shops must have something like that. Have you asked servocity?
It should be a pretty simple circuit to use a three position switch to send out a fixed PWM signal at each position. ...not that I would know how to do it though.
I am connecting my HF Gimbal board directly to a joystick and knob boxes from Servocity. How do I connect a three position switch if I do not have transmitter/receiver?