Punchout Catalog Restricted Items Approval Workflow

Hello,

We need restricted items in our Punchout Catalog to receive approval from our buyer before the approved purchase order is sent to the Punchout Supplier.  We use an automatic approval process for requests under $500.  Has anyone developed a process to catch restricted items and push them to an approver before the purchase order is submitted to the Punchout Supplier?

thanks.