I would think promoting just the display name would be adequate, right? It looks like you have a "submit" button in the repeating section.... so perhaps you could add another field for the "latest person" and promote that. The new field should be in a non repeating group in the schema, and won't need to be on the form. Then when you click submit, set the new field to the current person / group in the section where the submit button has been clicked. Which person / group are you talking about here, the Manager Approval section? Or the External Approval?
Hilary Stoupa