. . .
  open( my $fh, '>', 'myprogressdata') or die "bad open: $!";
  $fh->autoflush; # no buffering, print writes immediately 
  my $q = CGI->new( \&myhooksub, $fh );
  # You'll get control here only after CGI.pm is done
  # processing form and upload data
  . . .

##</code><code>##

sub myhooksub {
  my( $filename, $buffer, $bytes_read, $fh ) = @_;
  seek( $fh, 0, 0 ); # rewind to start of file
  printf $fh "Uploading '%s', %d out of %d bytes read\n",
    $filename, $bytes_read, $ENV{CONTENT_LENGTH};
}

##</code><code>##

  . . . 
  $that_ref_to_his_sub = ...  # copied from your 
  $his_other_data_value = ... #   call to new()
  . . .
  while( $buffer = more_to_read() ) {
    if( defined $that_ref_to_his_sub ) {
      $bytes_read += length($buffer);
      &{$that_ref_to_his_sub}($filename,$buffer,$bytes_read,$his_other_data_value );
    }
    print $fh_tempfile $buffer;
  }
  . . . 

##</code><code>##

#!/usr/bin/perl -w
use strict;
use warnings;
use CGI;
    my  $q = new CGI;
    print $q->header, $q->start_html( 
              -title => 'Upload Progress',
              -head  => meta({-http_equiv=>'Refresh', -content=>'3'}) );
    if( open( my $fh, '<', 'myprogressdata') ) {
        my  $progress = <$fh>;
        print $q->h2('Upload Progress'), $progress;
    } else {
        print $q->h2('No Data Available'), $!;
    }
    print $q->end_html;