navi2ch-net.el で、

(format (concat
"%s %s %s\r\n"
"MIME-Version: 1.0\r\n"
"Host: %s\r\n"
+ "User-Agent: Monazilla/1.00 navi2ch\r\n"
"%s" ;connection
"%s" ;other-header
"%s" ;content
"\r\n")
method file

したらいいんでね?