button.html

<div class="disqus-comments">                  
  <button id="show-comments" class="btn btn-default" type="button">Show <span class="disqus-comment-count" data-disqus-url="{{ trim .Permalink "/" }}">comments</span></button>
  <div id="disqus_thread"></div>
</div>

config.js

var disqus_config = function () {
  this.page.url = '{{ trim .Permalink "/" }}';
};

count.html

<script id="dsq-count-scr" src="//{{.Site.DisqusShortname}}.disqus.com/count.js" async></script>

load.js

$(function(){
  $('#show-comments').on('click', function(){
    var disqus_shortname = '{{.Site.DisqusShortname}}';

    (function() {
      var disqus = document.createElement('script'); 
      disqus.type = 'text/javascript'; 
      disqus.async = true;
      disqus.src = '//' + disqus_shortname + '.disqus.com/embed.js';
      (document.getElementsByTagName('head')[0] || document.getElementsByTagName('body')[0]).appendChild(disqus);
    })();

    $(this).hide(); // Hide the button
  });
});