Index pattern for all ccs deployments

Hi,

Within ECE we have multiple deployments. Most of them acting as backend deployments without kibana instances. And one deployment acts as frontend where we use all kibana features.
On ECE I setup CCS to all the backend clusters and created the index patterns in the frontend kibana.

Here is my question:

How can I create an index pattern that can search in all (or some) of the ccs index-patterns?

In an older elastichsearch stack on 6.8 we have (too) many indices and can search all of them when creating a * (all) index pattern. In our new setup we need to seperate out the data in the different ECE deployments.
But still I would like to be able to search all backend deployment indices from the frontend deployment through ccs.

Hope this makes sense, and thanks in advance for looking at my question.

Regards,
Patrick