i want to suggest that you make the box of:
Include external links by URL:
which can be find in the Exceptions tab
for links that site owner want to apply roles on.
i mean in the first tab: External Links
the: Settings for external links:
this setting be applied only on the links site owner provide on the Include external links by URL box
this will help a lot if the site owner want to apply the rel nofollow and rel sponsored for specific domains only.