Based on the previous answer, you may want to try to separate each request to be attended by a different CGI::upload_hook CGI. Then you can fetch the results of those different request making requisitions to them using GET or using Ajax to do it.

Anyway, doing like this looks like a great form of spending a lot of resources at the webserver. Maybe you should check which request size $ENV{CONTENT_LENGTH} shows and, hopefully being the biggest filesize, you should give a progress indicating how much time this file still needs to be processed until it finishes loading. Unless you're going to use Ajax (or any other technique to update the webpage without reloading it) it is useless to show the progress of each file being loaded.