check out following metalink note:
How To Reset a Purchase Order or Requisition From In Process or Pre-Approved To Incomplete/Requires Reapproval For Isolated Cases [ID 390023.1]
There are scripts listed that can be used to resubmit the document for approval by resetting the authorization status.
Another option is to try to forward the documents to the right person via [Purchasing Super User] Management > Forward documents.
Don't know if that would work in your case.