You can add arbitrary content to the login page. Edit
web.conf and update the
login_content setting. From http://docs.splunk.com/Documentation/Splunk/latest/Admin/Webconf
login_content = <content_string> * Add custom content to the login page * Supports any text including html
Given it can be HTML, nothing is stopping you from making one long line of tag soup. It will be harder to maintain, but you can present it to you users in a fairly clean manner.