Hi Ripon ,
As sunil mentioned, you can control it using Activity Profile. Keep it as the last activity in the shipment process.But billing split will happen if the header data like payer, incoterms etc... are not same.
Stream line your shipment process to achive the requirement.
We worked on it long back and i remember the process. It is as follows.
The Delivery Document for which Picking is completed will be added to the Shipment Document.
PGI will be triggered from the shipment using shipment status "Shipment Completed" . It can be achived again with Activity Profile.
Then use the shipment end status to trigger the billing using the suggestion provided by Sunil.
Regards
Vinu