Hi Manu,
You do not need an SAP BW system to fill the setup table. This activity can be done in the SAP ECC system.
Check out t/code SBIW and search for the path:
Settings for Application-Specific DataSources (PI) > Logistics > Managing Extract Structures > Initialization > Filling in the Setup Table > Application-Specific Setup of Statistical Data > Perform setup - Purchasing.
Best regards,
Sander