Add Maildrop to XML Gateway Transmission

We recently implemented Procurement and have set up our XML Gateway to communicate with vendor Office Max.  We would like to send the maildrop of the requestor on the PO line level so that when the items come into Receiving, they can be properly distributed by the mailroom.  I realize that we can create a custom map (we're using cXML_OrderRequest), but I was wondering if there were any fields included in that Oracle-provided map that we could use to pass this data along so that we don't have to create a custom map.  Thanks in advance.