Subdomain install without main domain control

Hello.

I’m trying to install a WP subdomain network for a customer.

WP will be hosted on server serverA (192.168.0.7).

My customer wants to point serveral subdomains he owns on different sites of the network (modelA.customer.com to model a section, modelB.customer.com to model b section and so on) but the main domain (customer.com) is already pointing somewhere else, and won’t move from there.

For testing purposes i set up a server to emulate serverA behavior, and i was able to correctly install the subdomain network by adding customer.com to my /etc/hosts file.

The install has a couple problems: a website named customer.com still exists, and the network control panel “belongs” to that site.

I don’t have any idea about how to remove that site, although I think i can solve the latter problem applying this change to wp-config.php:

//define('DOMAIN_CURRENT_SITE', 'customer.com');
define( 'DOMAIN_CURRENT_SITE', $_SERVER['HTTP_HOST'] );

Have you got any suggestions about how I can solve this? Will all this workaround work on the production server? Is there any simpler way to do this?

Thanks!