Is there a way for MRP to not aggregate supply for each item?

We buy wire on a real (600 meters per reel).  We cut the wire into different lengths so our inventory may consist of reels at different lengths such as 100, 100, 50, 50, 200.  We have a need for a 500 meter run.  MRP thinks we have 500 in stock but does not consider that we need 500 from one reel, not several reels aggregated together. 

We can use lot control which helps at the time of issuing the reel, but MRP still aggregates Qty available across the lots.

In the example about, we would need MRP to know we still need to order 500 meters.

Does anybody have a setup that works for them in this situation?