In WPMU, there was an option that would allow you to add the Buddypress feature on all multi-blogs (network blogs) installed under the main installation. Due to the great merge in WordPress 3.0, you can now enable BuddyPress in WordPress using the wp-config.php file as well.
Just open your wp-config.php file and add the following line.
define ('BP_ENABLE_MULTIBLOG', verdadero); This trick was shared by David Hunt in our Facebook community.
Note:Do this only if you want Buddypress to appear on all blogs in the system. It is not required.