What I have found out so far (see attached screen shot):
Choose the Output tab in the Bindings windows
Pick the correct monitor
Scroll to the control you want to attach a script to
Drag and drop the action into the middle windows
Select “Lua Script” in the “Value Source” in the right window
Here you can enter your Lua script.
Where the Trigger Value and the Action Value come from I don’t know yet. I suspect they are included in one of the Helios dll files.