[TYPO3-mvc] How to add to TCA searchFields when extending fe_user

[g4-lisz at tonarchiv.ch]

Hi there

My extension adds an additional field (relation to an entity of my
model) to fe_user.

Now I also wanted to extend the searchFields TCA from fe_user, so that
one can search for users related to certain objects of my model.

How can this be done? Is there some functionality from extension
manager, similar to addTCAcolumns()?

Cheers,
Till