Yes, it exists in my development branch of the wp-discourse-shortcodes plugin. I think it works better as a shortcode than by adding it as an option to the Publish to Discourse metabox. I’m not sure what is the best way to include this in the wp-discourse plugin. The shortcode could either be added to wp-discourse, or kept in the shortcodes plugin. In either case, I’ll get it ready to go soon.