Inventory in Diff UOM

My problem is as below...

1. User will book the sales order in BaseUOM(e.g Pcs)

2. Manufacturing output will be posted in Pcs, Box(100), SmallPack(50).

3. While doing warehouse shipment, User will fetch sales order lines
by using Get Source Document function.

4. At this moment shipment lines are in Base UOM, Bcoz Sales order
is booked in Base UOM(Pcs). But warehouse user wants to ship
the lines in different UOM(Box,SamllPack,Pcs), So that anytime user
can see what is the stock available in different UOM.

How can I map this functionality in Navision???