When a subscriber opts in to the list, do a real-time AWeber API check to see if they are already a member of the list and have a status of Stopped. If they are already on the list and have a status of Stopped, then do not add them to the list. add them to an alternate list.
IF email address exists on xyz list AND has a Subscribed Status of Stopped
then add the email address to abc list
The ideal candidate should have experience with AWeber's API. If you do not, then you would need to learn the API so that the above use case can be achieved.