I don’t know whether this will help but that’s how I’m carrying the testing right now.
I have a mysite.com which I obviously do not want to put offline so I set up a subdomain sub.mysite.com and simply install another instance of wordpress in there, than turn on multisite and at the end comes buddypress. Everything seems to be working just fine.
One important note: I’m operating the subdamain type of multisite url distribution system. Throughout tests I get to successfully set up blogs like blog1.sub.mysite.com, blog2.sub.mysite.com etc.
In the DNS settings panel I did nothing but setting the subdomain. No custem DNS records, nothing like that. Am I lucky or what? ??
