Multiple domains pointe to the same primarydomain, PLESK 12 change Docmentroot

multipledomains

1. Create a subscription for the additional domain in Plesk
2. Point the DocumentRoot to your primary Multisite domain
DocumentRoot /var/www/vhosts/primarydomain.com/httpdocs
SuexecUserGroup primarydomainuser psacln
<Directory '/var/www/vhosts/primarydomain.com/httpdocs'>
AllowOverride All
</Directory>
3. Disable PHP open_basedir
4. Enable PHP to run as FastCGI on the new DocumentRoot
<Directory /var/www/vhosts/primarydomain.com/httpdocs>
<IfModule mod_fcgid.c>
<Files ~ (\.fcgi)>
SetHandler fcgid-script
Options +FollowSymLinks +ExecCGI
</Files>
</IfModule>
<IfModule mod_fcgid.c>
<Files ~ (\.php)>
SetHandler fcgid-script
FCGIWrapper /var/www/cgi-bin/cgi_wrapper/cgi_wrapper .php
Options +ExecCGI
allow from all
</Files>
</IfModule>
Options -Includes -ExecCGI
</Directory>
5. Reload the domain configuration
reload the configuration for the additional domain (additionaldomain.com) and restart Apache:
/usr/local/psa/admin/bin/httpdmng --reconfigure-domain additionaldomain.com
/etc/init.d/httpd graceful

Thanks Robert Staddon
http://abundantdesigns.com/2013/06/06/multiple-ssl-certificates-for-wordpress-multisite-domains-in-plesk-11