Showing Excerpts of private posts to the public?

Instead of making my private posts completely invisible to the outside world, I would like to still publicly display their titles and excerpts on the homepage, indices, and search results, BUT I don’t want the public to be able to link to the full post.

I’m consolidating my website down to just a personal photoblog. I regularly post privately about things I still have a very public soap box on. So I end up repubbing a scrubbed down public version later. I would like to save myself the repetitive work by allowing my visitors to only view the excerpts of my private posts. The title link could go to the “You are not authorized to view this” fallout or simply not have a link at all. While me and my private audience would still have access to public and private posts equally.

Is this possible with an existing setting or plug-in? If not, how hard would it be knock it out? I would like to implement this feature to encourage myself to post more with less hassle, but not if I have to spend more time churning code than posts for awhile.