Escaping input for custom Twig Functions

I have a custom Twig function that will output a question mark icon with tooltip functionality from bootstrap. My Symfony twig extension class looks like this:

public function getFunctions()
{
    return array(
        new \Twig_SimpleFunction(
            'tooltip_icon',
            array($this, 'tooltipIcon'),
            array('is_safe' => array('html'))
        ),
    );
}

public function tooltipIcon($text, array $options = array())
{
    $defaults = array(
        'placement' => 'top',
    );
    $options += $defaults;

    return '<span class="glyphicon glyphicon-question-sign" data-toggle="tooltip" data-placement="' . $placement . '" title="' . $text . '"></span>';
}

Because I'm outputting HTML, I needed to tell Twig that my output is safe to render as is, and to not auto-escape it in a template. Otherwise the HTML would be escaped. However, I'm also taking user input and outputting it along with the HTML, so that needs to be escaped somehow.

For Twig filters you can do this by passing an additional option 'pre_escape' => 'html' to the filter definition, telling Twig to escape input before passing it to your filter. But for Twig functions, the pre_escape option has no effect. It won't escape the main function argument or any options passed in. In fact, this is briefly mentioned in the Twig documentation.

I was puzzled on how to manually escape input in a custom function, and couldn't find anything when searching. I turned to Stack Overflow where I was told I can manually call twig_escape_filter if I saved the Twig environment when it is initialized in my class:

protected $env;

public function initRuntime(\Twig_Environment $env)
{
    parent::initRuntime($env);
    $this->env = $env;
}

protected function escape($string)
{
    return twig_escape_filter($this->env, $string);
}

Now I can use the escape method to manually escape my functions input and options. The only thing that seems off to me is calling a global function to do the escaping, but it works.