Custom token claims for every client in a realm

I have a custom user attribute that I want to make
available to multiple clients in access token.
Is this possible somehow?

Currently one can define custom mappers for a single client via:(In Admin Console) Realm -> Clients -> client -> Mappers -> create
There I can specify a new mapper of type “user attribute” where I can refer to the actual user attribute, give it a “token claim name” (e.g.* > *“myattribute”) and specify whether this should be included in the access token.

This apporach however requires that I configure this for every client.
How a admin can map custom claims for all of his client manually.
It would make thinks a lot easier if it were possible to specify those mappers realm wise.

Each client has Assigned Default Client Scopes. I would edit for example profile scope (add your custom mapper there), so all clients in the realm with this scope will have your custom mapper automatically.