Simultaneous registration to 2 sites

I am developing a multisite whereby I am providing a templated blog for users for their customers/potential customers - on these sites they will be editors. I am also creating a site (within the multisite) for business training for the users (not their customers) and on this site they will be subscribers. Is there a way for them to register for the business site at the same time they register for their blogs so that it is seemless and they can use the same user id and password?