This is a way you could achieve multiple, variable inheritance. I'm interested in what kind of performance hit this might have.

gistfile1.php

<?php

class Base {
	function bse(){ echo "base <br />"; }
}

/* You would have to make a dependency-based loader
 * to keep track of class names.  Here, I'm just hard
* coding to show that it could work...
*/
$parent_class = 'Base';
eval("class _BaseA extends $parent_class {}");
class BaseA extends _BaseA {
	function a(){ echo "a <br />"; }
}

$parent_class = 'BaseA';
eval("class _BaseB extends $parent_class {}");
class BaseB extends _BaseB {
	function b(){ echo "b <br />"; }
}

$parent_class = 'BaseB';
eval("class _End extends $parent_class {}");
class End extends _End {
	function nd(){ echo "end <br />"; }
}

$ab = new End();
$ab->bse(); // base
$ab->a();    // a
$ab->b();    // b
$ab->nd();  // end