Have priviledged user(s) "signup another (anonymous) user", but block anonymous signups.

I don't know if the subject makes sense or not, but we need the ability to sign up people (using the ui on the signups tab) who are not (and likely will not be) users on the site, but I still want to force anonymous web users to register before signing up. I was considering attempting this w/ a workflow-ng rule(s), but wondered if it might not be a good feature for this otherwise fabulous module.