Freight Cost to Charge Conversion using charges already applied as a reference

I have a requirement to adhere to a total quoted shipping charge.  Basically when costs are entered on a shipment and the delivery is ship confirmed, those charges need to be evaluated against that quoted amount less any charges already applied.  Total charges must not exceed the quoted amount.

The problem is that when multiple line items are on a delivery, the pricing engine allocates the freight costs to each line and applies the modifier and formula to each individually and then posts data into the OE_PRICE_ADJUSTMENTS - which is where I am getting the summary of charges already applied to the order.