Summary

Mine was printed on a stock CR10Smart, PLA+, fits a 8mmx8mm latching switch from Aliexpress. Installed in the slider/potentiometer position and wired to the slider connector.
I'm running ELRS so that channel is being transmitted as a binary anyway when assigned to Channel 5 in the mixer. May take a few attempts to get the wiring order the right way around, Disclaimer: I shut off my radio a few times having it wrong and effectively shorting out the ADC or its Vref. radio undamaged, just shuts off when wrong pins bridged (simply power it on again to try another pinout), but all at own risk.