A possible solution, since this is the ubbdev forum, I think you have ubb.threads
ubb.threads uses files for a lot of inserts, header, footer, and forum specific headers/footers/inserts.
A solution could be to make a dummy forum, with no access to it for anyone, and use that header/footer/insert field for entering your file.
The file you are uploading, it is always the same file on the same place on your harddisk? If so, a scripted FTP solution would be the most usefriendly solution. Just hit the shortcut, and have a script upload your file.