This may be a European feature only seeing that you are located in Germany... I think someone would have definitely discovered this already if it was available.from the manual
USING THE PARKING AIDThe parking aid system can be set to activate automatically for when:
To enable the auto on feature, on the touch screen select, the Settings icon to access the PARKING AID SETTINGS pop-up menu. Select Automatic PDC ON.
- The vehicle’s speed falls below 6 mph (10 km/h).
- Drive (D) is selected for vehicles with an automatic transmission.
- Reverse (R) is selected for vehicles with a manual transmission.