I'm not sure if the tools you want to use support HTTP proxies, but if they (or some of them) do well enough, HTTP::Proxy could bring you a big step forward, as it relies mostly on LWP and should be easily hackable to support (nonpersistent) ftp connections.

Programming a real ftp proxy will be a bit harder, as I don't know of ready-made modules for that, you will have to kludge together something using Net::FTP on one side, and maybe Net::FTPServer on the other, but I guess you mostly want some dynamic command rewriting, so you can be off better by remotely controlling your Xbox in passive mode through one connection and connecting to your proxy in passive mode as well. That way, you can implement your "proxy" mostly as a variant of netcat, piping data between the two socket connections, although you still need to parse the control data.

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ;    # The  
$d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider
($c = $d->accept())->get_request(); $c->send_response( new   #in the
HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' #  web
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