View only a subset of roles when assign them to a user

In a realm I have an administrator with user management roles, so he can create new users into this realm, and I have custom roles, called for example “RoleA” and “RoleB”.
When this administrator assigns the roles to a new created users, I want to show in the available roles list, only “RoleA” and “RoleB”, and not all default roles of Keycloak (I don’t even want roles filtered by client).
So, my goal is to have in the list ONLY RoleA and RoleB.