I think the best way to do this is to move the object to a specific folder and set up permissions on that folder to allow the read only access. You probably at least have a library folder set like this so can emulate that.
We used to do this with skeletons so only selected experience users could work on and change them.
Permissions are a bit complex in Intralink so you may at the least need the admin manual or a friendly PTC guy that still remembers how to set up a system.
