conf problem

Hi,

I'm faced to a conf pb that neither current nor new Conf design can solve.
For the SimpleEntity vortex package, I need a place to store a map
entity-base-class-name => path to class. What for?

For instance, I have in vortex/store an entity called Item.php.
I want to extend it in my own app, but keep everything else from 
vortex/store. As the Item class is included and instanciated in many 
places, I cannot extend it without copying the whole vortex/store dir 
and modifying all files, simply to change the include_once line and set 
my extended class path.

The solution I think to is this one:
* have a map 'base class name' => path in conf
* use include_entity(), defined in SimpleEntity
   that uses this map to load the right class.

For instance for my item, with this in conf:
   item => app/myapp/MyItem.php
include_entity('item') would include my extended class.

The problem is that I need that different packages using SimpleEntity 
place their conf in the same path:
  vortex/store should have a conf SimpleEntity containing
    'item' => vortex/store/entities/Item.php
placed in simpleentity domain
(conf path being simpleentity/class_path/item)
  and in my app I need to overide this value with
    'item' => app/myapp/MyItemp.php
with the same conf path :/

Any solution ?
-- 
Jean-Christophe Michel