Cascade the proxy

Hello, Could i cascade the ftp-proxy so that i can install one in the internal net (where the users have to connect to) and one in the dmz. A problem there is, that we have an other dns-root in the internal net than in the dmz, so the hostname-lookups fails. Since many years we use Squid for HTTP and for download FTP, but now i have to brak my brain about the ability of uploading FTP to hosts in the Internet. Have someone a sample of the config-files? Kind Regards Markus Weber