Hide extension elements from "Add capella element..." menu

Hey,
So I have an extensible element that is hooked via ownedExtensions. However, I would like that the element is not proposed when I select “Add Capella Element…” on the related extensible element. (The element is managed automatically, there’s no need for the user to create them manually) What is the kitalpha/capella studio way to do this? Do I just edit the generated child creation extender, or is there a kitalpha way, e.g. an annotation or whatever?
Cheers,
Felix

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