Refining Groups and/or Lists

We have a regular Monday morning meeting for a 20 minutes coaching session.
Registrants for the meeting filled in a form and were tagged with a single tag. 64 total tagged to date. We have 576 total contacts.
I want to send a broadcast email to the 64 LESS the participants for that Monday meeting. In the case of this week 64 contacts minus 8 = 56 to receive the email broadcast.
I do not want to remove this weeks participants from the tag group as this is a weekly recurring meeting.
I tried creating a Group but the list still contains all 64 of the tagged contacts.
Does anyone know how to remove those who participated from the 64 tagged contacts, use the list in a broadcast email and then reset for the following week back to 64?
Greatly appreciated.