Allocation of Freight in JDE 9.2

We are currently implementing JD Edwards 9.2.  We are struggling to solve a Business Requirement where our Buyers want to see the amount of Freight at the PO Header Level and also allocated at the Line Level by case or weight.  Additionally (and here is the tricky part), they want to be able to adjust individual line allocations manually.  So they might add to the allocated amount on one line and deduct it from another line while keeping the total amount of freight at the header level the same.  This is a process that they can do in their current