Adding Volt functions dynamically

I would like to try to use addFunction method of Phalcon\Mvc\View\Engine\Volt in controllers for some actions.

I tried to do this but I couldn't exactly achieve what I wanted.

    // Setting up view component
    $di->set("view", function() use ($config, $di) {
        // Initiate service
        $view = new View();

        // Set views directory
        $view->setViewsDir("../apps/backend/views/");
        // Return service
        return $view;

    },true);

    // Setting up volt
    $di->set("volt", function() use($config, $di) {
        $volt = new Volt($di->get("view"), $di);

        $volt->setOptions(array(
            "compiledPath" => "../vars/volt/",
            "compiledSeparator" => '_',
            "compiledExtension" => ".php"
        ));

        return $volt;
    }, true);

    // Register volt engine
    $di->get("view")->registerEngines(array(
        ".volt" => $di->get("volt")
    ));

Everything seems OK (view files are rendered) with the code above except when I would like to get an output of a view file.

    $output = $this->view->getRender("controllerName", "actionName", array("viewVariable" => $myViewVariable), function($view){
        $view->setRenderLevel(View::LEVEL_LAYOUT);
    });

This returns string(0) ""

If I change my setup to this, I can get output of view file and all other view files of controller / actions are rendered correctly.

    // Setting up the view component
    $di->set("view", function() use ($config, $di) {
        // Initiate service
        $view = new View();

        // Set views directory
        $view->setViewsDir("../apps/backend/view/");

        // Set template engine
        $view->registerEngines(array(
            ".volt" => function($view, $di, $config){
                $volt = new Volt($view, $di);

                $volt->setOptions(array(
                    "compiledPath" => "../vars/volt/",
                    "compiledSeparator" => '_',
                    "compiledExtension" => ".php"
                ));

                return $volt;
            },
            ".phtml" => "\Phalcon\Mvc\View\Engine\Php"
        ));

    }, true);

Unfortunately the code above doesn't allow me to acess Volt through DI

I also tried to set volt while setting view component but it the same problem occured.

    // Setting up the view component
        $di->set("view", function() use ($config, $di) {
            // Initiate service
            $view = new View();

            // Set views directory
            $view->setViewsDir("../apps/backend/view/");

            // Set template engine
            // Volt
            $volt = new Volt($view, $di);

            $volt->setOptions(array(
                "compiledPath" => "../vars/volt/",
                "compiledSeparator" => '_',
                "compiledExtension" => ".php"
            ));

            $view->registerEngines(array(
                ".volt" => $volt,
                ".phtml" => "\Phalcon\Mvc\View\Engine\Php"
            ));

            // Add to DI
            $di->set("volt", $volt, true);

            // Return service
            return $view;

        },true);

I'm trying to add Volt to DI so I can do this in a controller method (action)

    // Get volt template engine
    $volt = $this->getDI()->get("volt");

    $volt->getCompiler()->addFunction(
        "customFunction",
        function($name) {
            return "Hello {$name}";
        }
    );

Am I doing something wrong here? Why can't I use getRender()?