Yes, using switcher events.
In rundown control, go to window - preferences - switcher events. Using the drop-down menu, look for audio variables and select one of the functions. Assign that function a number, this is the number you will use in your custom control.
If using Caprica:
To create the custom control, look for overdrive, then look for switcher events. Type in the same number, insert.
If not using caprica, please respond with switcher type and version number.