Reverse User Syncing

Hey, great plugin. Was just wondering can the the sync work in reverse?

We have 8 Wordpress sites, ranging from version 3.1 to 3.4.1 and we wanted to have somewhat of a single sign on service to access all the sites.

So is it possible to signup on a sub site which syncs back to the master site? Or is it just a trickle down from the master site to all the subs?

Also what happens when a user changes their user information on the subsite, will the information be reflected on other sites?