Multi Domain (new site with domain not subdomain)

I'm working with the Multi Domain Plugin. When i do "ADD NEW SITE" i only have the option to add a subdomain of all the domains i included.

I would like to know "how to add a new site with domain" and not a subdomain.

Exemple
Now: Add new site:
name.arixoportunidad or name.arixbarcelona.com

I would like: Add new site:
arixbarcelona.com

I attached screen.

Thanks for your help.

Jordi