When not logged into Facebook, the Facebook comments plugin shows a dropdown "Comment using..." which lists the following options:

Facebook; Yahoo; AOL and Hotmail.

I'd like users to only be able to comment using Facebook and none of the other services. It sounds like this can be changed via the "Comments Box" settings (see the heading "How do I enable users to comment using other login providers?" on this page https://developers.facebook.com/docs/reference/plugins/comments/
but there's no "Settings" on the plugin that I see. Should there be? Or is it not possible to change?