Actually, it looks like App Order approval is available for EHP5.
http://help.sap.com/fiori_bs2013/helpdata/en/57/7f3c52c638b610e10000000a44176d/content.htm
This seems to be the correct component, but it is archived: PURCHASEORDAPPR
1954756 - Release Information Note for Approve Purchase Orders (FIORI PURCHASEORDAPPR 1.0)