Add usergroups to Event Reminder on the frontend

[Cyboman]

It would be a nice idea, if I could add users or usergroups manually and/or automatically to the event reminder function on the calendar frontend (for permitted users/mods/admins).

I'd like to always inform my community (or parts of it) f.e. 1 week or 3 days before events start. Maybe this could be added on the event creation mask, if permitted users create new events.