FTP Proxy ..?

Anybody using a ftp proxy out there My clients need to put to an external ftp site. Rather than allowing them to connect through a nat firewall I would like them to use a proxy, in a similar fashion to web proxy , for the connection and have the proxy perform the put and get on their behalf. I have come across the SuSE proxy-suite but it doesn't seem to do what I want, in that it seems to be geared for reverse proxying a ftp server. Can anybody help ? Alan Dawson