Skip Billing - Do Not Ship for Customer-provided Inventory

Summary:

We need a way to include items on invoice at a query cost, but not shipped.

Content (please ensure you mask any confidential information):

Our customers sometimes request items to include in the medical kits we replenish on their behalf. The kits must be complete for medical reasons, but since the customer provided them, we do not want to bill the customer. The same items are also offered to customers; therefore, they are in PIM. However, since the customer owns them, we do not want to decrement inventory.

Aside from excluding them from the Sales Orders, I haven't found a good solution. Has anyone experienced this previously?