buddypress and multisite

Hi, I am wondering if it is possible to install buddypress in a multisite (sub)blog only (not the main blog). I have tried to do this but the buddypress-bar is listing my main site as home link not the buddypress blog. Profilepage, messages and so on are directed to the main site too. Am I doing anything wrong or is a buddypress installation only in the main multisite possible?

Thanks for any tipps …

edit: ok, just saw that buddypress can only be activated network wide ..