Right now the web parts/pages in the FBA Pack are just coded against Microsoft's membership provider model, which unfortunately does not support password expiration. You'd have to modify the FBA Pack to no longer use the membership provider and access
the database directly. (Or create your own membership provider that provides this functionality).
Then you'd just have to create a custom login page that checks if the password is expired before letting them in, and force the user to change their password if it is.