examples.js

/**
 * Example using a Deferred object
 */
(function(){
  var deferred;

  $(document).on('click', '.show-scores', setupOnce(function(){
    // $.getJSON returns a $.Deferred object
    deferred = $.getJSON('/scores.json');
  }, function() {
    deferred.done(function(json) {
      // fancy score handling
    });
  }));
})();

/**
 * Prepare a modal box or a template once and fill it in at each invocation
 */
(function(){
  var modal;

  $(document).on('click', '.modal-trigger', setupOnce(function(){
      modal = new Modal();
  }, function() {
      modal.title = this.source.title;
      modal.show();
  }));
})();

setupOnce.js

/**
 * Runs `setup` on the first invocation
 * Runs `callback` on each invocation
 * @link https://gist.github.com/lavoiesl/6241939
 *
 * @param  Function setup
 * @param  Function callback
 */
function setupOnce(setup, callback) {
  var ran = false;

  return function() {
    if (!ran) {
      setup.apply(this, arguments);
      ran = true;
    }

    return callback.apply(this, arguments);
  }
}

Any reason why you're creating a second closure? You can do without the once function.

function setupOnce(setup, callback) {
  var ran = false;
  return function() {
    if (!ran) {
      setup.apply(this, arguments);
      ran = true;
    }
    return callback.apply(this, arguments);
  }
}

I have no idea. Thanks :P