Tracking inventory for final shipping materials-outer shipping box-

does anyone have any suggestions on how to automatically track inventory usage (use inventory and trigger po suggestions) for final shipping materials, i.e. outer shipping boxes that are used to ship different configurations/amounts of customer shipable parts, since the outer boxes are not contained on any bill of materials.

we have 10 different sized final shipment boxes (therefore 10 different part #'s) that we use to ship our customer ordered parts.

depending on the number of different customer ordered parts on a specific sales order that we are fulfilling, we make the decision of which box to use at final shipping, so these parts are not in any bill of materials.

we are using epicor 9.05.606