Field Creation in Target Node

Is there any function which creates fields in target node without having that field in sender payload in SAP PO Mapping ?

For Example:

Sender payload:

a
 a1
 a2

Receiver Payload:

a
 a1
 a2
 a3
  a31
  a32

In the above example I sent a payload with fields a1 and a2 but i want a3 field in the receiver, How can i get the a3 field in receiver without providing in sender ?