This is my terrible manual workaround right now. (Maybe this answer will prompt you savvy developers out there to write a better one?)
I run the following querry in the database to determine who isn't signed up for the newsletter:
FROM qa_users u left join qa_usermetas m
on u.userid = m.userid
where m.content is null
This returns a list of user id's for all users who don't have the newsletter. Then I go into the qa_usermetas table and add them.