SD-PS Integration

We are implementing SD-PS integration to our client.

In Sales Order, we are assigning WBS and delivering material by CNS0. Problem is in document flow,you can't see delivery document number.

but while creating delivery CNS0 system pop up for sales order number.

I understood that LP type of delivery is w/o reference of sales order but I am searching a possible way to achieve this document flow.

Secondly, I am invoicing through sales order(order related) with bill plan.

Pls suggest a wayout.

Scenario is :

We have project (may have service material and finished material), at the time of reaching one milestone client invoice for particular milestone to customer.

Seeking for suggestion.