You can add additional IP address via the "Network" tab in the virtual machine configuration. separate them with a comma, like this.
"1.1.1.1, 2.2.2.2, 3.3.3.3, 4.4.4.4, 5.5.5.5, 6.6.6.6, 7.7.7.7"
Virtuozzo Containers are powered by OpenVZ the same technology that Proxmox uses.