Form generated from form cache displays, but missing name and value attributes
Figured it out. Use form_get_cache() to get the cached entity, throw that into $form_state, and then use drupal_build_form() to put it together again.

    $form_state = array(
        'submitted' =&gt; FALSE,
        'rebuild' =&gt; FALSE,
        'cache' =&gt; TRUE,
    );

    // Pull the entity object from cache.
    $cached_form = form_get_cache($form_build_id, $form_state);
    $myentity = $cached_form['#entity'];

    $form_state['myentity'] = $myentity;
    $output = drupal_build_form('myentity_form', $form_state);