Dear Vic Phillips,
I think you can also check here the concept of Dynamic Safety Stock.
Dynamic safety stock does not create the planned order once it decrease from a fixed point.
Means you can keep your safety stock as 1000000 pcs. But keep you dynamic safety stock as 540000 pcs.
So once your stock do not fall below the dynamic safety stock your requirement will not be created. But once it will fall the requirement of 1000000 pcs will be created.
Please check that scenario. As i think i am correct. Here you can use MRP type PD.
Regards,
Saurabh Kumar