@toneflacone - you can do exactly what you want in the “Hello, home” section of the app:
- go to hello home by clicking the red number (or empty dialog bubble if there are no new notifications) in the upper right of the main app screen
- click the gear icon on the bottom of the screen
- Click “Add Action” at the bottom of the list of whatever actions are there
- Give it a name
- Under “Turn on these lights or switches” select the light you want to come on
- scroll to the bottom and click the “+” next to Additional Settings
- Select "Automatically perform <whateverYouNamedIt>
- Select Everyone Leaves and select the presence devices
Then click done