How do I get the Processor's (approver) email?

I added Send Mail steps to the standard Purchase Requisition workflow (ECC6), WS00000038. These mail steps were added on the paths for Approved and Rejected. These both work well, but they were easy to set up in the mail step because I was able to choose &_WF_INITIATOR& as the Recipient. However, I need to add another Mail step to send email to the Approver (I know this is a common request), but I have no idea what to select in the drop down for "Recipient Type" and "Expression" in the mail task. There is no "%WF_APPROVER%".

What do I select there in order to send the email to the User I have set up in the IMG as the owner of the Code?