You can try to use Server Push (see your CGI.pm man page and examples) to serve out a progress bar. Basically the solution can be a server push for each uploaded chunk of file.

The solution should be similar for mod_perl, using the hook provided by Apache::Request, as stated by Kanji.

Please note that i didn't try it and that man page says "Only Netscape Navigator supports server push. Internet Explorer browsers do not".

Hope this helps.
Bye, Valdez