Just replace the douche head with this nozzle and enjoy. The water valve on the nozzle is a very convenient feature.

Drawbacks:

• Made out of aluminium, so the cleaning (e.g. from the aluminium (hydr)oxide) is a bit tricky. Looking for a stainless steel nozzle.
• Does not have any means to fix it in place. A harness mounting feature would be a good add-on

The douche nozzle can be bought here.