This BuddyPress plugin by Adam J Nowak allows the creation multiple sidebars, just name your new sidebar the same name as the Buddypress Component and it will show up when that component is displayed. So you can have separate sidebars for ‘Activity’, ‘Members’, ‘Groups’, etc.
You can also name a sidebar the same name as any page and that sidebar will automatically show up on that page. Prefabricated sidebars include Home and Blog. The Blog sidebar will appear on single and archive blog pages.
Plugin homepage: http://hyperspatial.com/wordpress-development/plugins/buddypress-sidebar/