Option 2 is your best bet. This dosn't seem too klunky.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

package Tk::MyText;

require Tk::Text;
use base qw/Tk::Text/;
Construct Tk::Widget 'MyText';

sub ClassInit {
#  print "ClassInit [@_]\n";
   my ( $class, $mw ) = @_;
   $class->SUPER::ClassInit( $mw );
   return $class;
}

sub InsertKeypress {
   my ( $w, $char ) = @_;
   #     print "@_\n";
   if ( $char !~ /\d/ ) {
      return;
   }
   else {
      shift->SUPER::InsertKeypress( @_ );
   }
}
1;
############################################
package main;

my $top  = tkinit;
my $text = $top->MyText->pack;
MainLoop;
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