SAP Business Object for purchase order with the position as a key field

Hello,

I want to create an event when I save a new purchase order postion and get as well the order number as the order position in the container of my workflow.

But I only found the Object BUS2012, wich has only the order number as a key field.

But I need the order position too. Is there a possibility to enhance this Object, when I want to use the transaction SWEC for connection of the business object?

Thanks a lot!