When Netbeans knows about variable type, it shall offer option to create function with it:

Code:
Class Example
{

  protected function one()
  {
     $date = new \DateTime;

     $this->doSome($date); // Cursor here and activate hint dialog
  }

}

Hint dialog:
Create method "doSome($date)" in Class "Example" (Example.php) // NOW
Create method "doSome(\DateTime $date)" in Class "Example" (Example.php) // NEW
...

Note: both options will be available