How can you set the default override approver on a PO

Summary:

We have certain purchase orders that need to be routed to a specific individual for approval. Is it possible to set the override approver for a specific BU to a specific user? This user would be stored in either a value set or approval group so that this individual could be changed without updating any code.

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We are currently on on the latest cloud version of Oracle and could update this in a sandbox but I'm not sure how to do the lookup query.