IDEA: Offer customers a cost savings on parts only if they allow you to use the scrap.

Tell your customer you have scrap that is perfectly acceptable to use for making some or all of their products if they will give you the approval for the switch.  Tell your customers that you can cut their costs if they allow you to use scrap material. Where and how the product is used will help dictate the answer. There is someone out there who would like a cost reduction and will not care about your firm using scrap.