The easiest way to control comments is to create a 'Genaral Comments' or 'Guestbook' post.
- Create a post called 'Guestbook'.
- Make sure comments are allowed and set the way you want.
- Explain what your comments policy is. (It can be as simple as: "Keep comments on-topic or post them in my 'Guestbook'.)
- Publish the post.
- Add a link to the post to the sidebar.
Note: This won't work if your blog comments are restricted to team members. In that case create a blog specifically for comments and link back to the team blog.