You can't. At least not without tweaking the whole Content Viewer's framework, which is only available for Enterprise customers. And even then, I think it would be highly advised not to mess with this carefully growing convention in its user interface. Of course, you can turn each article/page completely into HTML content and script your and your reader's brain out. But as a best practice, you can't and shouldn't. The user needs to retain their sense of 'position' in a publication and each article.
