constructor.php

<?php

class BaseClass
{
    private $var;

    public function __construct($injector)
    {
        $this->var = $injector;
    }

    public function show()
    {
        echo $this->var;
    }
}

class InjectorBlocker extends BaseClass
{
    public function __construct()
    {
        parent::__construct('blocked');
    }
}

class GetInjectorBack extends InjectorBlocker
{
    public function __construct($injector)
    {
        BaseClass::__construct($injector);
    }
}

$object = new GetInjectorBack('it works');

$object->show();