Leave request approval access to non employee (no PERNR)

Hi

We have an exceptional case where Approver can select a non employee (No pernr, but has SAP ID) to approve leave request from subordinates.

We would like to send a work item as well as email notification to non employee , so that person on can approve/reject employee time on manager behalf.

When I have debug portal Leave request component while submitting EE leave request,  it was throwing an error message that says "No approver exist"

Any thoughts or recommendation to address this?

I could think of maintaining mini master for such non-employee scenario, however, this will result in introducing new process to business  and thus seeking your suggestions here.

Thanks in advance