FTP server behind firewall?

[Gilles]

On Wed, 16 Apr 2008 22:06:24 -0400, Jon Radel <jon at radel.com> wrote:
>What control do you have over the firewall?  One of the cleaner
>solutions would be to run an ftp proxy on the firewall, such as that
>supplied with pf.  See ftp-proxy(8) or
>http://www.openbsd.org/faq/pf/ftp.html

Unfortunately, the router/NAT firewall can be neither replaced nor
tweaked, since it's a modem/router provided by our ISP.

Actually, we don't necessarily need an FTP. Whatever solution to send
files is fine, provided I can add this feature in a VB Classic client
application.