use warnings;
use strict;

BEGIN{ 
    package ConstErr;
    use Tie::Handle;
    our @ISA = qw(Tie::Handle);
    sub TIEHANDLE {
        bless \my $i, shift;
    }
    sub PRINT {
        my $r = shift;
        print grep { $_ !~ m/constant/i } @_;
    }
    package main;
    tie *STDERR, 'ConstErr';
}

use constant PI => 3.14;
print PI, "\n";
use constant PI => 1000;
print PI, "\n";