Change page URL sent to Universal Google Analytics when using Google Tag Manager

How can I change the page URL that is sent to Universal Google Analytics when using Google Tag Manager? Without Google Tag Manager it's really simple. You just have to add ga('set', 'page', '/my/custom/url'); before ga('send', 'pageview');.

Your Google Analytics script needs to be like this:

<script>
  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
  })(window,document,'script','http://ift.tt/1pxBd1V','ga');

      ga('create', 'UA-XXXXXXXX-X', 'auto');
      ga('set', 'page', '/my/custom/url'); /* Set my custom URL */
      ga('send', 'pageview');

</script>

How can I do something similar using Google Tag Manager?