Custom mapping from Ariba to Ariba Network

We had a customization to map phone field(in the adhoc ship to address) from Ariba to S4 and Ariba to Ariba network. We have successfully mapped Ariba to S4. But to map from Ariba to Ariba network we are facing few issues. For multiple line item through standard mapping the phone is flowing correctly but for single line item the standard mapping is made at header level hence, the phone is not flowing to Ariba network. Did any one did this cutomization before?