Hi ricmcd,
I think RSVP Pro gets you perfecty covered
You just need to configure RSVP Pro to send reminders to all Attendees (in the Reminders tab of the component configuration).
Then create an event and set there the number of hours prior to the event you want the email reminder to be sent.
Finally go to RSVP Pro -> Sessions and click on the Attendees column for your event. There you can add a new attendee which you can search just writing down the username.
With this you will be able to configure the system as per your needs