Office 365 New Domain??

I have a client that has a free gmail account they use for a small business the client has another business with exchange online plan 1.

They want to add a new domain and stop using the gmail account.

Since the gmail account is free how do I create this in the existing o365 business portal as another domain?

And bring over the email data?

Do I use this even though they dont have a business domain for your Google App

http://technet.microsoft.com/en-us/library/dn568114.aspx