Receipting sub contracting

How can I get MRPeasy to recognise parts are not new when I receipt a Sub Contracting purchase order? It seems to add the items to stock and not take them off when I dispatch the finished products to our customer. For example we make a part then send to a sub-contractor for plating, sub contracting is in the routing for the part. I raise the SC purchase order through the source on the customer order so its all linked.