I see this post is older but hopefully my answer may still be of use.
I just read your posting and I would think a VMI stocking system will help with this. Depending on the system in place you can determine stock by either available quantity and or weight of raw material. I have some clients that manage their stock on a daily basis and it is a mixture of determining the weight of raw materials, as well as the quantity of product taken from inventory. Some solutions handle this all through barcoding procedures. One good example is aggregate companies; they can determine their availability of raw materials based on the poundage/tonnage and height of raw material.
Hopefully this was informative, if not please disregard.