Yes guys you heard that right. Internally in MCS we had this option for quite a while but as of last week customers and partners can now do it as well and we (Microsoft) fully supports it.
For instructions check out this piece of content by one of the UE writers: http://community.office365.com/en-us/wikis/sso/configure-filtering-for-directory-synchronization.aspx
Until later,
Henrik Walther