Ariba Requisition Push to SAP Lessons Learned

Hi - curious if anyone can share some lessons learned on integrating Ariba Requisitions into SAP?

We require pre-PO Funds Commitments to be generated in SAP as this triggers financial approvals. Our SAP team believes the best way of doing this is to integrate the Ariba Requisition into SAP which then automates the Funds Commitments rules.

We are looking at creating a Custom Approver that will make a Web Service call into an SAP Create Requisition BAPI.

Any information on how you designed a similar solution is appreciated. Custom Approver, or built into Submit Hook, or designed elsewhere? How do you error handle, etc.

Thanks!