If users are going to be opening the document in a server environment, they won't be able to see the Variable Overview anyway. If you want to restrict this for users who are opening it in the thick client, you would need to check out Document Properties --> Security and implement a combination of security settings and section access (to define who is a User and who is an Admin). I'm not positive, but I think that if you disable Document Properties for Users, it will also disable the Variable Overview.
Regards,
