Adding - Ship parts,returns and charges to the same sales order

Hi

We are on R12.1.3 and Our business process is as below

1.Customer calls in Service center for field service repair and an SR is generated by the service coordinator

2.A task is generated and assigned to the technician.(technician does not own his van stock nor has any PDA device)

3.Technician calls the customer and understands the problem and thinks some parts are required and asks service coordinator
  to ship the goods to the customer site.

4.Service coordinator ships the parts to the customer site.

5.Technician visits the site and completes the repair and  unused part is returned to the service center through courier.