Usage of Position Hierarchy with Multiple Positions for same user

We have a requirement to map Reapproval Rules in Purchase order Approval.(12.1.3). Currently  Purchase Order approval is through Position Hierarchy. Reapproval for certain attributes  like Amount, Unit price , etc is being controlled by Standard functionality -  by setting Tolerance form. Certain Other Attributes like  Frieght, Payment terms etc alos triggers reapprovals and going through entire PO Hierarchy. ( Eventhough Automatic appovals can be managed by PO Workflow customization, As of now this option is not being considered. Future plan is to go for AME Approval and same can be mapped there).

Now as a workaround we are trying to create a specific hierarchy with two people, so that any changes can be routed to them and can be approved  within them. But we face a challenge here . These people already exists in other hierarchies and have some limited approval ( say 500000USD). But the PO's which undergoes reapproval  may exceed this amount Say until 10000000 USD. And  For this approval has to go for VP or president. Even though Amount is not altered in these PO's, Only other attributes are changed, these PO's need not go again to Top level.