I have a custom template for my email reminders for Meetings. I do not use the default template.

I am trying to set up an automated workflow to send out my custom email template to Meeting Participants, but when I choose "Instant Actions/Email Notification/Create Email Notification,"  the only recipients available in the To field are internal (Creator, Owner, Owner's Manager). I want to send the notification to external people in my Contacts list who have been invited to this meeting. How do I do that?