You could overload the stringify operator to get the current value of the object.

#!/usr/bin/perl -w
use strict;

package LazyBool;

use constant THE_BIT => 1 << 9;
use constant RAND_SIZE => 1 << 16;

use overload 'bool' => sub {
    my $self = shift;
    $self->{value}();
};

use overload q[""] => sub {
    my $self = shift;
    return defined $self->{peek}() ? $self->{peek}() : "not defined";
};

sub new {
    my $class = shift;
    my ($value,$self) = (undef,{});

    $self->{value} = sub {
        defined $value ?
        $value :
        $value = THE_BIT & rand(RAND_SIZE) ? 1 : 0;
    };

    $self->{peek} = sub {
        $value;
    };

    bless $self, $class;
}

1;

package main;

use strict;

my $foo = LazyBool->new;

print "\$foo is $foo", $/;

print '$foo is true', $/ if $foo;

print "\$foo is $foo", $/;
[download]

It does essentially the same as your example code but just hides away the calls to $foo->{peek}() in the stringify operator. It seems the logical way to do it as you'll only be 'looking' at the value of $foo in a string context (well that's what $peek seems to allude to). That's what overloaded operators are for right?
HTH

broquaint