$form->add('postage_option', 'entity', array(
    'class' => 'AcmeBundle:PostageOption',
    'property' => 'name',
    'multiple' => false,
    'expanded' => true
));

{% for option in form.postage_option %}

    <div>
        {{ dump(option.vars.data) }}
        {{ form_widget(option) }}
    </div>

{% endfor %}