It would be a good idea to have 'announcement' posts.
These would be like a post with no URL (like you can do) but with the added feature of being 'stick'y to the homepage of the topic. They would also be 'unscoopable'.
This way a top owner could slip in an announcement or useful tip to the topic's readers.
Thanks. I have now done this. Works well.
AdminScoop.it (Admin, Scoopit) commented
Right now, there is a way to create a post with no URL to stick to the top of your page. If you scroll over the post after it's already posted, there is a STAR icon that you can click to stick the post to the top of your topic.
Many curators use this to add a little note to the beginning of their curation, including other web links, a summary of what might be found on the page, etc.
Though this post can be rescooped, it's a great way to do exactly what you are looking for.