One invoice per sales order for delivery related billing

Dear all,

Here is my requirement:

One customer is requiring us to issue only one invoice per sales order.

Given that we can have multiple outbound deliveries per sales order the prerequisite is to ensure that all outbound deliveries have status goods issue posted.

Sales order 1

Outbound delivery 1

Outbound delivery 2

Outbound delivery 3

Outbound delivery 4

Invoice 1

Invoices have to be generated automatically so is it possible to implement a check to ensure all outbound deliveries linked to a sales order have status goods issue posted?

Thanks.

Anthony