Design Business with wordpress

I read this post:

and it says:
"your clients most likely will never even know that they are on a Multisite installation."

So that is something Im trying to achieve, but after installing wpmu and plugins and almost ready to go, noticed the sign-up process with wpmu that new users go to register to the main domain.

And have searched for a way out of this default wp behaviour to really be able to mask that they are part of a network of sites.

And that new users don't get confused when registering a new account.

So how can this be possible? to really be able to hide they are part of a network?

Thanks a lot.