Approval workflow for Purchase Orders created from Multiple Requisitions

Summary:

Hello,

We have a requirement to initiate PO approval workflow if the PO amount is beyond a certain threshold from the Requisition approved amount. This is not that big of a deal if the PO and Req have a 1:1 relationship. The real issue is when POs are created from Multiple requisitions (where the Requisition # on the PO shows "Multiple") need to be compared to the combined total of all the Requisitions to see if the PO amount exceeds the combined total of all the requisitions by a certain threshold. Is there a way to handle this in the PO