Same Username/Email Address - Different Sub-blogs

Hi there,

I have noticed that if a user tries to sign up as a user on one site in WPMU and is already subscribed to another site that he cannot use the same username or email address. Is there a way around this?

These two sites may have nothing to do with each other and the user may not even know that they are connected. I thus would like to find a way to override this - is this possible?