Standard PO ammendment approval

We need some suggestions as what other companies are doing for the following requirement to be met and see if we can meet the same within Oracle.

PO Approval limit for a Procurement Specialist: 100,000

PO Approval limit for a manager: 1M

PO Approval Limit for a Director: 10M

1. Create a standard PO for 5M --> It goes to the manager and then to the director for approval and gets approved

2. Amendment done to the PO to increase the amount by 50,000 --> goes again through the entire approval hierarchy to the director before it gets approved

The requirement is that since the amendment amount is only 50,000 the procurement specialist should be able to approve it. Right now Oracle does not do this and to change the workflow logic is next to impossible it seems.