Trigger when Mission Control activates?

I'd like to trigger a macro when I do a 4-finger swipe down on my trackpad. Since this gesture can be mapped to Mission Control or App Exposé I thought I'd try to use "Trigger when this application: Mission Control activates".

I added the application to the trigger from the Mission Control icon in Applications.

I'm guessing Mission Control is activated at some system level rather than a real application. So is there any other way I can trigger when Mission Control, or App Exposé are invoked?