Unsubscribe a lead not in database

Hi,

How do I create an unsubscribe option for an email address that is not in our database. 

For example: I am trying to provide a user who is associated with a lead within out database an option to unsubscribe? Can I just add this email address to a static list and use the Member of list - not in - static list? Or is there no way to achieve this? 

Thanks,