ideas for ftp proxy over 2 proxy servers

wanted to see if anyone has ever done a similar type project or encountered code that could do this:

i have an ftp client and server sitting in separate locations and i have 2 freeBSD boxes (one per location) that i want to proxy the ftp connection through. the problem i have so far encountered is that trying to pipe hits the application layer and attempts to kick off a connection from the remote proxy box to the ftp server and from the ftp client to the local proxy box. instead of proxying one connection, i get two broken connections.

is there anyone out there who's done this before or seen code that does?

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nik