Formatted Search : Order Weight to Order Freight Window

Greetings:

I have the following scenario:

I have created a UDT that has 3 columns - code, name, price. Client has pre-defined freight cost based on the total weight of the order (example - 5 lbs. = $4.56). UDT.Name = weight, UDT.price = freight charge. Is it possible to put a FMS on the amount field of the Freight Charges window that looks at the total weight of the associated Sales Order and selects the proper price based on weight?

Thanks in advance,

Aaron