Block 'new registration' updates in activity stream (BP 1.7)

How do I stop new user registrations appearing in the activity stream in BP 1.7?

I have tried this plugin:

and this hack:

and neither seem to do the trick. I'm guessing it's because they're only designed for versions up to 1.5.1

I can't seem to find anywhere else that does this.

Any ideas how to go about doing this?