set up WPMS in subdomain outside root folder

I'm wanting to set up multisite network in subdomain.domain.com(for added security) but doing so creates new sites as

newsite.subdomain.domain.com.au

which won't resolve without a tweak to apache, but does not look nice as a site address (site.domain.com looks okay)

would you know what tweaks need to done to htaccess file / apache to get WP to create new subdomain sites.... newsite.domain.com?