Multisite with "www" in domain name

Hello,

I have a wordpress multisite site I'm working on, and they want the url to have the "www" prefix (currently it's without). Can this be done with without having the "www" show up as part of the URL for subdomain network sites?

The site is: http://genesisshelter.org/ and they want it to be http://www.genesisshelter.org/ , but they want to have subdomain network site like this: http://spanish.genesisshelter.org/ (not like this: http://spanish.www.genesisshelter.org/).

What's the best way to achieve that?

Thanks!