Assign some Drupal user roles as group administrators and other Drupal user roles as group members

Currently, og user roles only allows automatically assigning a user to a specific Drupal user role when he/she joins a group.

For example, I would like to have when any user, who has an Editor drupal user role and joins a group, be automatically assigned as the group's Group Admin. Also for any user, who has a Reader drupal user role and joins a group, be automatically assigned as a regular group member.

anyone?