Since consigned item does not update the average cost of an item, we cannot calculate correct Sellin

Let's say we bought/received 3 different phases;

1. Bought 10 qty at 6 USD - 1-Jan-14 (Not on Consignment) - Average Cost Price = 6

2. Bought 10 qty at 4 USD - 10-Jan-14 (Not on Consignment) - Average Cost Price = 5

3. Bought 40 qty at 2 USD - 25-Jan-14 (On Consignment) - Average Cost Price should become 3 but it will remain 5 only since we bought/received the last delivery on consignment.

We calculate our selling price as 30% above our system cost price. But because of enabling consignment feature our selling prices are incorrectly higher.

How do we make sure that our average cost price gets updated even for consigned items so that our selling price calculations are correct.