Disable subscribing to threads in some forums

[Odysseus]

I'd like to add a new feature to my board:

In the Admin Panel, the Administrator can disable subscriptions of threads for forums .
This means, that the users cannot subscribe to any thread which is in the specified forum.
When moving a thread to a "disabled" forum, all subscriptions to this threads are to be cancelled as well.

The admin should be able to set this to every forum individually . (!)


Reason:
I have two forum s on my board, in which only very large threads are posted (1 - 1000 posts, then closed). The e-mail notification might cause deadlocks to the post-table when precessing such large threads.


Is there a hack available with which I can do this?