Prevent invoice being mailed to EDI customers

Hi, everyone.

Most of our customers receive their invoices from us via regular mail.  However, there are a handful of them that we have set up to receive their invoices via EDI.

The problem lies in the fact that we will still print out copies of their invoices for our own use, and these travel around our company for a while before being filed.  I want to make sure that nobody accidentally folds that invoice up and mails it to the customer.

Ideally, the solution would be 2-fold.  Firstly, all invoices printed for EDI customers would print with a giant EDI watermark on them.  Secondly, the address on these invoices would be shifted to the side so that they do not show through the address window on the envelope.  This way, the watermark makes it very clear that the invoice is for an EDI customer, and anyone that ignores this would still be unable to mail the invoice.