I currently am using a script that runs once a week that will go through the CSV you can download from each campaign, and email managers a list of direct reports who are still missing their training.
The only downside to this method is the CSV does not have the campaign start and end dates in any of the columns. Would it be possible to have the campaign start/end dates added to the CSV we can download?
I suppose an even better option would be to have the ability to email managers a summary of their direct report training status during campaigns. As much as I use the "Remind users who have not completed" options I've found it more effective to make sure their managers are being notified as well. Plus it's a good CYA element to make sure the KnowBe4 admin isn't on the hook for ensuring everyone completes their training on time within reason.