It is now possible to add a separate charge to pick and pack fee's by adding individual packaging charges on a product level.
You can do this in bulk using the product upload feature in Products > Extras , or on an individual basis when you create or edit a product in Products Overview
Please navigate to Picking / Storage Cost column:
This will now add £0.50 charge to every unit ordered, so if it is a 10 unit order - it will add £5.00.
The packaging fee is displayed separate when client invoice is viewed: