Well yes, the function is called with a MouseEvent as one of the arguments, so you could use the "arguments" object to access it.

What I was thinking of, was something along the lines of:

  // From http://ejohn.org/blog/partial-functions-in-javascript/
  Function.prototype.curry = function() {
    var fn = this, args = Array.prototype.slice.call(arguments);
    return function() {
      return fn.apply(this, args.concat(
        Array.prototype.slice.call(arguments)));
    };
  };

  els = document.getElementsByTagName('li');
  for(i=0; i < els.length; i++){
    els[i].addEventListener('click', function(x){
        alert(x);
    }.curry(i), false);
  }