BCC to sender

I have been tasked with providing a common signature for all email in our company. This signature will include a company logo and other embedded graphics (links to social media, etc.) along with a confidentiality notice. This signature must show up on the “sent” item and be archived with the full signature on it.

We have GroupWise 8 (8.0.3, with plans to upgrade to 2014 in a month or so). We have a single domain, single post office (83 mailboxes in use) with a single GWIA and Web Access. Mobile devices are synched through GroupWise Mobile Service. Email is archived through GWAVA Retain. The endpoints we need to have use this common signature are Windows, OS X, iOS, Android and of course the Web Access.

The global signature works with the exception of the requirement "the sent email must have the signature" (proof that the confidentiality notice was attached).

Is there a way to enforce sending a blind copy to the sender that would have the "global signature" attached?