Implementing additional level of approval for Complex PO

Hi,

We have a requirement of implementing additional level of approval for complex PO.

Requirements:

1.     If the Complex PO is linked to a Project at PO Line level, then the Key Members “Project Manager” of the Project linked to the Complex PO will be the “Pre-Approver” for the Complex PO.

2.     If the Complex PO is not linked to a Project at PO Line, then the DoA of the Cost Centre on each line should be used to determine the first approver with the appropriate delegation to pre-approve the Complex PO.

Please let me know if anyone has implemented the same or knows any better way to implement the above requirement.