Reversing changes to a PO once in "In Process" status

 Is there a way to get a PO out of "In Process" status and back to the original state before changes were made and sent back out for approval?  I have tried in test instanecs rewinding workflow and canceling the workflow but thsi doesn't do what i need it to.  Canceling the workflow only freezes the PO and rewinding it to the beging does just that and start the workflow all over again.  I need to get the PO back to the last approved state.