Option needed to Invoice from single part shipment and multiple part shipments.

Option needed to Invoice from single part shipment and multiple part shipments.

E.g.  Currently we make sales order let save for 10000 cases of different items.
Part Packaging and Shipments are made during the month.  Sometimes the sales order is not closed for 2 month.

To make invoice for part shipments is like manual work we have to club the 2 or 3 shipment and than create the invoice manually. Currently no option is available to create invoice from Shipment.

Curently when we create an Invoice the quantity is picked up form Sales order.  But if an option is given to create Invoice from 1 shipment or multiple shipments it would resolve our problem.
 
Secondly if there are 4 shipment delivered we should be able to get total of all 4 shipments together.   
This is an extremely urgent requirement as the operators are creating lots of error while creating a manual invoice.