posts preview in homepage and category archives

I need to show all my user (even not-logged ones) a preview of all posts with title and abstract (or excerpt). Once they click it if logged ok.. if not logged pay!
By now I'm using the tag-more to hide not-logged users all the content below and works good.
But... my site has about 200 authors and I can't ask everyone to use the tag-more 'couse sometimes they forget it or don't even use it.
Any chance to avoid tag-more and manage previews in homepage and archive pages?.. waiting for a better authors world..