[Zope] how to prevent URL access to an external method?

I need to do something on the filesystem, which requires unrestricted python, so I created an external method. The problem is that anyone can call that directly via URL, so I added a permission check. Even then, users with the sufficient permissions can call this via URL, which I don't want them to do. I only want them to have access indirectly from other pages (such as a page template that will pass sane parameters). Is there anyway to do this?   Thanks, PL