You'll need to configure your host to be able to handle multiple IP addresses. This is often called "aliasing", and can generally be configured through an IP alias or dummy interface. You need to read your operating system documentation to figure out how to do this. Once your have the host configured to accept the additional IP address that you wish to offer a virtual FTP server on, use the <VirtualHost> configuration directive to create the virtual server: <VirtualHost 10.0.0.1> ServerName "My virtual FTP server" </VirtualHost>
You can add additional directive blocks into the <VirtualHost> block in order to create anonymous/guest logins and the like which are only available on the virtual host.