I tested to see if something like this would work with just CGI and a staging page, but straight from the CGI docs is this:

    2.  The optional second parameter is the starting value for the field
        contents to be used as the default file name (-default).

        For security reasons, browsers don't pay any attention to this
        field, and so the starting value will always be blank. Worse, the
        field loses its "sticky" behavior and forgets its previous contents.
        The starting value field is called for in the HTML specification,
        however, and possibly some browser will eventually provide support
        for it.

My idea was that a user could enter the full path to the file, which would have to be done by hand to avoid using the 'browse' button. Then forward that filename and path to the next page. This works fine, but the file in question can't be auto added to your final real upload because of the browser issue mentioned in the above documentation clip.