Sales Invoice requires UPDATING

We can modify the invoice in the customize invoice however when we enter an invoice it only defaults to what you have set information to enter.

We do not use shipping date or salesman name.  Our customers require a PO number field as well as a customer Work Order field. 

What good is it when we customize the invoice template if we cannot actually enter the data require by the customer on the invoice.  Currently we have to enter all additional required data in the comments field.

PLEASE MODIFY YOUR TEMPLATE so it is more user friendly allowing customers to receive data required.  Thank you.