XF 1.5 Watch Forum when creating New Thread - Settings OR Custom Template Edit


In my board, the users have their alert preference set as

default_watch_state = ‘watch_email’

So I understand that users watch the thread they start and they get email notifications as well.
Additionally I want them to watch the forum in which they start the thread.

Is this possible with a setting in admincp or custom template edit.
Thanks in advance for the reply.