Access to Groups and Permissions - Users configured via LDAP

For all those who has configured Matillion ETL Users using LDAP, how did you assign them to Groups and provide granular permissions? 

 

The External User Configuration window allows LDAP Group users to be mapped only to Roles (like Server Admin, Global Project Admin, API , Read-only). What if I would like to map them into more granular groups with Reader/Writer Privileges? How do you do that?