How can I override a capacitive touch on-off switch?
If you are an electronic hobbyist, you could build a circuit that simulates a human finger: 

You can get a big electrolytic capacitor (e.g. 2200uF 50V) which has the size of a human finger. Then you can move this capacitor on the switch with a servo motor, or you can try to electrically connect/disconnect one terminal to earth to trigger a capacitance change.