Adding Push-To-Talk (PTT) / Mute to 3-pin XLR Cable
Set the switch mode to push to open and connect it across the signal lines. (pins 2 and 3)
releasing the PTT will mute the microphone signal by shunting it.
So, connect pin 4 to pin 2 and pin 5 to pin 3
With a 20 foot cable this may not work very well. if you are allowed to modify the base make the same connection internally instead.