gistfile1.aw

<?php
class Foo
{
	public function __set($method, Closure $callback) {
		$this->methods[$method] = $callback->bindTo($this, $this);
	}

	public function __call($method, $args) {
		return call_user_func_array($this->methods[$method], $args);
	}

	private function doSomething() {
		return "Hello World!";
	}
}

$test = new Foo;
$test->sayHello = function() {
	return $this->doSomething();
};

var_dump($test->sayHello());