Here’s the use case. We have the Learner’s direct manager imported via SSO into a Learner Custom Reference field. 
On the Dashboard we are creating, we have a required filter with limited selected “Managers”, searching against Learners where that “Manager” appears in their Reference field.

I’d like to add a “Learner” filter so they could find the Learner they care about, but right now it shows everyone in the sublicense. Is there a way to limit the choices of a filter to only those that that meet the criteria of another filter?