Hi Thomas,
Another way to go is to develop a bit on Nicholas idea of another field. I understand you are importing the CO's through API, not from SFDC.
Therefore, you could create another field in the CO, for instance 'Follow-up email date" and set the values of that field prior to import in the import file (= event date + 7)
The you would simply run a daily batch that would select every lead with a CO which "Follow-Up Email Date" is yesterday.
You would also be able to use this field in the velocity script for filtering.
-Greg
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