You can create an Abstract Soap Server by creating a class with the magic method 
__class() to handle any request.

Of course, this isn't ideal in a web service world but it's a possible.

SERVER (AbstractSoap.php)
==================
<?php
// class
class AbstractSoap {
	function __call($name, $args)
	{
		return array('Operation'=>$name, 'Arguments' => $args);
	}
}

// start server
$server = new SoapServer(null, array('uri'=>'http://jromero.me/AbstractSoap'));
$server->setClass("AbstractSoap");
$server->handle();
?>

CLIENT (client.AbstractSoap.php)
==================
<?php
$client = new SoapClient(null,array("uri"=> "http://jromero.me/AbstractSoap",	
"location" => "http://someurl.com/AbstractSoap.php",));

$Authentication = new stdClass();
$Authentication->Username = 'user';
$Authentication->Password = 'password';

$Person = new stdClass();
$Person->FirstName 			= 'Javier';
$Person->LastName 			= 'Romero';

$response = $client->AddAccount($Authentication,$Person);
print_r($response);
?>

After 15 years without any feedback, except for a comment that
shows that this is already possible, I think we can close this as
WONTFIX.