Inventory items linked to rework costs don’t need to be in ‘unassigned’ stock location.

Inventory items linked to rework costs currently need to be in ‘unassigned’ stock location. I need to reduce the inventory level of a client's packaging via a rework cost with a linked inventory item, but the client's storage is billed by location so, if I move their packaging to 'unassigned' location, the system won't bill them for the pallet space. I have been told that I would need to switch the client's whole storage model to volumetric to make this work, which would be a lot of time and effort. Alternatively, I need to unlink the inventory item from the rework cost and then manually reduce the inventory item every time the rework is performed, which is time consuming. The other option is to move the inventory item to 'unassigned' and manually invoice for an extra pallet every storage period, but that is not practical to remember every week.