Edwin,
I am using 1.9.4... going to the course setting page and changing the Availablity to not available to students... will not uneroll the students, so their work should still be there. They can't see it but it is grayed out for teachers or admins. I believe they should still be able to get in and grade work that has already been completed. When grading is completed, if necessary, you can just change the setting back so students can get back in. The listing wasn't even available in the "My Courses" block for the student on my site.
Hope that helps.
Paula