Did something similar on my Graupner MC-10 some years ago JB
Didn't like the price of their '4 Channel Add on module'.
So I rummaged around in the 'bits box' and found three miniature switches; push button (Honk Honk😁), ON/OFF (Lights, Smoke etc), 3 way ON/OFF/ON (for two functions TBD), and a small 10K pot (crane/turret traverse etc). In those days the switching was done at the RX end by microswitches on servos or my home brew decoder / relay board.
Worked a treat an' did'n cost me nuffink😊
Odd! All TXs I've investigated had 10K pots!
Cheers, Doug 😎