I have a client who wants to turn off open_basedir as he using cross domain includes. I have recommend against doing this for security reason but he has insisted.
I was initially looking at modifying the ./conf/vhost.conf file for each domain and adding the open_basedir config but found a quicker way.
add a file called. /etc/httpd/conf.d/zzz_turn_off_open_basedir.conf
and add these lines to it.
php_admin_value open_basedir none
Save it and restart apache.