# In the various classes :
__PACKAGE__->setupMemoizedSubs(
   methodname => sub { 
                 my $self = shift; 
                 #... do resource-intensive stuff .. },
   anothermethod => sub { ... },
)

# In a common base class :
sub setupMemoizedSubs {
    my ($class,%args) = @_;
    no strict 'refs';
    while (my ($name,$sub) = each %args) {
        my $private_element = "__memoized_$name";
        *{"${class}::$name"} = sub {
             my $self = shift;
             $self->_set($private_element => $_[0]) if @_==1;
             return $self->_get($private_element)
               if $self->_is_set($private_element);
             $self->_set($private_element => $sub->($self)); 
             $self->_get($private_element);
        };
    }
    use strict 'refs';
}

# Somewhere else
$object->methodname("pre-computed value"); # set the value
$object->methodname();  # Gets the value we set

# Or if we omit the first one...
$object->methodname()  # Actually calls the method