Forward to a Friend Unsubscribe

Our organization does not allow us to store leads who have not explicitly opted in. If an internal AE forwards an email to a contact that is not in our database, we cannot house it in Marketo. Out of the box, Marketo sets new leads that receive a forwarded email as unsubscribe. If we delete them from Marketo for compliance, and they fill out a registration form, will they come into the system as unsubscribed due to durable unsubscribe? What are some work-arounds? If we have a campaign that reverts the unsubscribe to "false" and then delete them, will this solve the issue? Any and all suggestions welcomed! Thanks!