Copy distance from route to stage in shipment order

Hi, experts

Since only the stage in shipment order is relevant for shipment cost calculation, is there any way to copy the distance from route to stage in shipment order, or making the route distance is relevant for cost calculation.  the customer is not using stage master but only route master data.

I think in both ways user-exit is needed, but I'm not familiar with the technical things. so any help would be greatly appreciated!

thanks !