[HOWTO] Attendeelist with not registered Joomla users

There are situations, you want an attendeelist, but for different reasons, the attendees don't want an account on your site.
A possible "solution": your admin registers these persons with invalid emails (@invalid.com). Think to disable the email.
You don't need more: only firstname, lastname, username. Then the admin from backend or the event creators from frontend are able to add the attendees (which sent their will to participate an event).