loader.js

(function() {
  var jQuery = window.jQuery,
      frag = document.createDocumentFragment(),
      js = document.createElement('script'),
      css = document.createElement('link'),
      head = document.getElementsByTagName('head');

  if (jQuery === undefined || jQuery.fn.jquery !== '1.8.2') {
    jq = document.createElement('script');
    jq.href = "//ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.js";
    jq.type = "text/javascript";

    jq.onload = function() {
      jQuery = window.jQuery.noconflict(true);
    };

    frag.appendChild(jq);
  }

  js.async = js.src = "//mysite.com/the-other-script.js";
  js.type = "text/javascript";
  js.onload = function() {
    /* Call your init function with our jQuery variable. */
    window.MyWidget(jQuery);
  };

  css.href = "//mysite.com/my-css-file.css";
  css.type = "text/css";
  css.rel = "stylesheet";

  frag.appendChild(js);
  frag.appendChild(css);
  head.appendChild(frag);
}());

document.write('<div id="the-widget-container" style="display:none"><!-- all your other stuff here? --></div>')