How about if you had a "contact the admin" link with each post? Like, normally there is a "contact the admin" on the page, and often there is a "contact the author" on each post. Seems to me being able to contact the admin on each post would satisfy this request?

That would be perfectly acceptable. However, it should be accompanied by an admin screen that lists the links of the potentially objectionable posts.

If you really want to be full featured, it would take the admin into a screen to make the post private and set the rights on it so that the blogger couldn't make it unprivate.

Also some sort of mechanism to communicate with blogger about why the admin pulled the post, as well as communication on what to do to get it reposted.