The Wiki page on this topic states that using the following:

<?php $form = $this->zfcUserLoginWidget(array('render' => false)); ?>

will return a login form.

This is not exact. It will return a ViewModel with a loginForm variable that contains the login form. One would then have to do the following:

$loginForm = $this->zfcUserLoginWidget(array('render' => false))->getVariable('loginForm');