How to modify Pagination on Posts

Some of our posts are restricted by s2Member, and some are not.
This means that when a non-logged-in visitor uses the “previous” and “next” buttons at the bottom of each post, if the next or previous post happens to be protected by s2Member, they get redirected to a page which tells them they tried to access a restricted area.
This is obviously not satisfactory.
Can you suggest a resolution please?