Not pretty, and perhaps there are better ways, but this may get you started anyway:

#!/usr/bin/perl -w
use strict;
use IO::Pty;

my $pty = new IO::Pty;
my $slave = $pty->slave();

my $pid = fork();
die "Couldn't fork: $!" unless defined $pid;

if($pid){  # dup STDOUT to Pty and run external program:
    $pty->close_slave();
    open(STDOUT, ">&",$pty)||die $!;
    system "perl blackbox.pl";
    print "\cD"; # send ^d to end 

} else {    # this is your monitoring process
    $pty->make_slave_controlling_terminal();
    print "*$_" while <$slave>;
    exit;
}
__END__
[download]

Works for me on Linux.