As you may know, there are different methods to apply discount to a customer order line, no matter if it’s an standard sales part or a package part. If your requirement is based on qty for the part, and not in a Group Discount with a Basis Min Order Value (this could be achieved easily with the assignment of a Discount Group in Package Part), then you could use a Sales Price List (as most generic option) or a Customer Agreement, in case specific Agreements are set by customer and delivery conditions.
Without specific requirements, it’s difficult to suggest the most appropriate method, but hope above helps you.