Email verification multisite.

Here is the scenaro. Users sign up to get there own site.(blog)

they create a site called “PeterSite”. The site is created. Peters site sends peter an email letting him know what his username and password is and where he can login. eg: With me so far? Good!

The problem of multisite is, Peter is added as a user to his site automatically and to the main site automatically. (two sites) So peter gets another email from the mainsite with username, password and login address. Except this time the login address is for the main site. eg

How does one stop this email from the main site?