There is no way to submit forms or upload files in (standard) gopher. Instead,
you can use a command line client to post on Gopherchan. This client is written
in python, and should run on reasonable default installations.

The communication protocol itself is a plain HTTP mime-encoded form post;
chan.py uses urllib2 to send data.

First, download chan.py somewhere, and customize the settings in the header
section:

    nickname = 'anon'
    delpass = 'lofasz'
    handler = 'http://port70.net/cgi/post.cgi'
    editor = 'vim "+set tw=70" -c startinsert'

Please use word wrapping at 70 columns for your message text (lines will be cut
off at 80 anyway).

Usage: ./chan.py [-n nickname] [-d delpass] [-m message] [-f file]
    [-k killpostno] (-b board | -t threadname)

You can either post on a board (OP) or in a thread, so you have to specify
either -b or -t.

To post, a message has to be specified, in one of three ways:
 -m "on the command line"
 -M in_a_file.txt
or, if these are omitted, the external editor will be invoked, with the name of
a temporary file appended to the command.

Uploading a file is not mandatory. The source file can be specified by -f.

After having made an OP, your thread will receive a "thread word". To make CLI
usage easier, threads are identified by short random words instead of ID
numbers. To make a reply in any thread, you specify its thread word after -t.

Posts can be deleted by specifying the board with -b and the post number with
-k. Deletion passwords have to match.

Obviously, having a CLI interface makes abuse quite easy. Pretty please go easy
on us :)