Web service using eprocurement punchout vendor

We have a customer wanting to utilize a punchout vendor, but they want to interface the requisitions to us via webservice based component interface.  The desired behavior is that the user interfaces a requisition through the webservice (Based on the requisitions component), the requisition goes through approval framework, once it is approved it can then be picked up and auto sourced.  Currently the regular purchasing auto sourcer only brings PO's up to a staged status, however the Eprocurement auto sourcer will completely create the PO and do all of the associated actions (This is what we want).  Is there a