Dynamic SAP Send Port in BizTalk

in a customer scenario i have to use a dynamic SAP user for creating a purchase order. the purchase order will be created with calling a BAPI in SAP.

the customer logs on into a client app to create the PO. his username and password will be embedded in a xml envelope and used to configure a dynamic SAP port as described HERE.

1. create an expression shape to set the sap address.
2. create a sap message with the user properties.