Need to add PO Requisition preparer as approver in AP Invoice approval rule

Summary:

We have created the AP invoice approval rule for freight and Misc lines if the amount exceeds 20% it should go to buyer as approver. Now there is a change required to approver should be the requisition preparer. 

How to add the requisition preparer as approver in the resource.

Content (please ensure you mask any confidential information):

We would like to route invoice approval to the preparer of the Requisition related to the Invoice PO in case of adding Freight and Misc line in the invoice instead of PO Buyer. The available resource rule routes to the Requisition Requestor where in the preparer is to validate the FREIGHT and MISC in our business use case.