How do I forward an assuresign document if I do not know the recipient's email upon sending out the envelope?

At the time of sending out the envelope, we do not know what the email address of one of the recipients (Recipient B) would be as another recipient (Recipient A) would have to forward it to that entity. How would that work? If we assign Recipient B's fields to Recipient A, can Recipient A simply forward that document to B to sign?