muiltisite and several fixed subdomains : possible ?

Hello !

Well here the point.

Have a multisite install to perform but want to keed several fixed sub domaines which can eventually be separate cpanel accounts. ex :

install : mysite.com ==> multisite

fixed : support.mysite.com (forum for example)

Is it as simple to forbid the "support" subdomain in WP options ? Will that work ?