Controlling default settings across the entire network – possible?

I have WP multisite installed with the Buddypress add-on. I’ve been able to resolve spam signups across the site using a simple question+answer. What I don’t know how to do is control comment spam across the individual blogs that people are creating. I’d like the option “Users must be registered and logged in to comment” to be checked by default for everyone (again, across the entire network of blogs). I’m thinking if I can get this working, problem should be solved.

Is there anyway to set this up so that new blogs have that option automatically checked?

Thank you!