Multi-domain, Multi-network for BuddyPress

I have WP 3.4.2 with multi-site subfolders + BP 1.6.1.

So as people are admitted to my network they will have accounts like
domain1/members/user1, domain1/members/user2, etc.

I would like to have multi-domains + multi-networks such that I can have
domain2/members/user4, etc as well as
domain3/members/user6, etc.

in such a way that all the users can participate in groups and forum across the networks (each of which has its own domain) and can friend each other across networks (domains), all using the same WP+BP installation.

That is I want to have a combination of multi-domain and BP multi-network capabilities while using multi-site subfolders. That is, for practical reasons I don't think I want user1.domain1, user2.domain1, user3.domain2, user4.domain2, user5.domain3, user6.domain3, etc.

What combination of plugins and settings, or any code/database changes would you recommend to achieve this objective.