Hi,
You can create PO for main vendor and use partner functions to keep different vendor codes with that main vendor code(XK01/XK02)
Main Vendor= V
Goods supplier(GS)=V1
Invoice payee(PI)=V2
For more refer how to use partner functions for different business transactions by same vendor code.
http://scn.sap.com/thread/3364925
Regards,
Biju K