In my previous blogpost, the Sonoff worked, but was lacking a manual override. The switch could only be triggered by Domoticz. Since it also has a physical push button (connected to GPIO0 (D3)), it can be switched by hand. All that needs to be done is:

1. Create a new switch device in the Sonoff
2. Enable 'Rules' in the Tools / advanced settings
3. Create a rule
4. Change the On/Off commands in the switch parameters in Domoticz