Hi Wolfgang,
If the order is flowing from CRM then you can enhance that interface so that while creating the order the input will be in such a way that ECC will create the order for set where in higher level item will be set and child will be small box. The child item will be free of charge (item category TANN). For extra items new line item will be created and that will be charged.
I assume that either IDoc or BAPI is used for creation of sales order. For both methods it is possible to enhance.
Hope this will help you.
Thanks
Atul
