Freight costs in header of purchase order distributed automaticallyto items

Hi!

I have entered "Freight" condition at header level (percent) in the purchase order; if I entered let's say a percent of 20% for freight in header PO, the system puts 20% at every item. What I would like to do is to enter total value for "Freight" in header PO and the system to distribute this value to all the items in the purchase order as per their value or per their quantity. I don't want to enter "freight" for every item in the purchase order. Could you please tell me how should I do that?

Thanks.