Instantiate an object without calling its constructor in PHP

Update: ReflectionClass::newInstanceWithoutConstructor is available since PHP 5.4!

Another way will be to create a child of that class with and empty constructor

class Parent {
  protected $property;
  public function __construct($arg) {
   $this->property = $arg;
  }
}

class Child extends Parent {

  public function __construct() {
    //no parent::__construct($arg) call here
  }
}

and then to use the Child type:

$child = new Child();
//set properties with reflection for child and use it as a Parent type