It would be better if there was a way to do it without hacking the Discuss code, but if that isn't possible, your way looks fine to me.
Thank you again for posting the mod.
I have implemented the code on my site but I was confused slightly as to a couple of things.
discuss.enable_notifications_moderators -- "yes/no" value?
setting_discuss.enable_notifications_moderators, "what do I put here?"
setting_discuss.enable_notifications_moderators_desc "what do I put here?"
Thank you in advance!