Ah, I wasn't sure just what aspect of the code you were most interested in. A more traditional approach to inside out objects goes something like this:

use strict;
use warnings;
use Data::Dump;

package Counter;

my %data;

sub new {
    my ($class, $start) = @_;
    my $lu;
    my $self = bless \$lu, $class;

    $data{$lu = "$self"} = {count => $start};
    return $self;
}

sub add {
    my ($self, $value) = @_;
    $self = $data{$$self};

    $self->{count} += $value;
}

sub get {
    my ($self) = @_;
    $self = $data{$$self};

    return $self->{count};
}


package main;

my $ctr = Counter->new (7);
print "Start: " . $ctr->get () . "\n";
$ctr->add (3);
print "End: " . $ctr->get () . "\n";
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which gains the data hiding without losing Perl's normal OO support.

The largest downside I see with the code you suggested is declaring all the anonymous subs in the constructor - that just doesn't scale well to anything other than toy code and is syntactically much nastier in my view.