Not sure about your current setup, but I can explain how we have thing set up for when we might need to send the first invite out numerous times. We do not use batch email sends, instead, we use a combo of static lists, smart lists, email assets, and smart campaigns.
When the campaign is not synced to our CRM:
The initial list of attendees is imported into the program and then added to a list.
The invite is created as an email asset (not a batch program)
A smart campaign is created to distribute the email and change everyone's status to "Invited"
Now, if you have people that you want to add at a later date, you have a few choices, but essentially, if you add them to the program and their status is just "Member", you could re-use the smart campaign from above, as those people won't have run through the program before (hopefully!). You could also add them to a separate list (say, Invite 2) if you want to know who was invited in different stages, and then set up another smart campaign to send to the second invite group.
Was this what you were getting at? If not, as mentioned above, a description of your setup would be helpful.
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