BuddyPress.org

OK, so I used the code from Xevo in this thread in a custom functions.php in my child theme. It redirects all calls throughout all the WPMU blogs to signup.php to the BP register page, which should help you do what you want, if I understand correctly.

One thing this hack doesn’t do is to pick up any changes to the register slug in wp-config, though, so you’ve got to remember that if you change it.