Configure KM folders for no feedback permission

We have the following customers needs for KM folders.

- By default, users can't feedback on a document, but they can read documents.

- Some users can read documents and make feedback (and this implies that they can read their previous feedback, that's not a problem).

- Administrators can read/write documents and write/read all feedbacks on a document.

So the problem we are facing now, is how to disable feedback by default, so that basic users can't see the link "Give feedback " on the command menu, and they can't see the feedback on the details screen.

We have configured the service permission for a folder that basic users haven't any service permission (we assume that feedback service is included) in this folders (and no permissions are inherited) or just layout service. But the fact is that the user can read the document (this is OK for us), but they can also feedback this document (that's what we don't want...).

Any idea if it is possible to configure? What's the possible solution?

Thank you very much