How do you limit permissions of Instructor to add students to the "main" course section.

[cvolpe1]

Hello,

At Princeton University we allow Instructors to add users with a "student" role to their course for specific reasons (unofficial audit).  In some of our courses, there is the "course" section as well as additional sections (labs, precepts).  Student enrollment is often in both the course as well as the other sections.  When am Instructor uses +People tool, we only want the "course" section to appear as an option, not the complete list of sections.  Does anyone have a way to limit the list displayed?  I do not see it as a Permission.

Thanks so much!

Courtney