Index: model/interceptor.php
===================================================================
--- model/interceptor.php       (revision 0)
+++ model/interceptor.php       (revision 0)
@@ -0,0 +1,27 @@
+<?php
+/**
+ * Interface for api_model_factory interceptors
+ */
+ interface api_model_interceptor {
+
+     /**
+      * Used by the interceptor to instruct the factory
+      * whether it wants to intercept the instantiation
+      * of the object
+      * @param string classname the factory should create
+      * @param boolean true if the interceptor wants to intercept
+      */
+     public function intercepts($classname);
+
+     /**
+      * Used by the interceptor to create and return an object from the factory.
+      * Called only if the intercepts method returns true. Has the same signature
+      * as api_model_factory::get()
+      * @param $name string: Model name.
+      * @param $params array: Parameters in order of their appearance in the constructor.
+      * @param $namespace string: Namespace, default "api"
+      * @return api_model_common
+      */
+     public function get($name, $params = array(), $namespace = 'api');
+ }
+
\ No newline at end of file
Index: model/factory.php
===================================================================
--- model/factory.php   (revision 11512)
+++ model/factory.php   (working copy)
@@ -11,6 +11,9 @@
  * The result will be an object of api_model with the given named params.
  */
 class api_model_factory {
+
+    private static $interceptors = array();
+
     /**
      * Model Factory
      *
@@ -23,6 +26,13 @@
         if (class_exists($namespace . '_model_' . $name)) {
             $name = $namespace . '_model_' . $name;
         }
+
+        foreach ( self::$interceptors as $interceptor ) {
+            if ( $interceptor->intercepts($name) ) {
+                return $interceptor->get($name, $params, $namespace);
+            }
+        }
+
         if (count($params) == 0) {
             return new $name;
         } else {
@@ -30,4 +40,16 @@
             return $class->newInstanceArgs($params);
         }
     }
+
+    /**
+     * Register an object that can intercept the request made to
+     * api_model_factory::get() and return a different object.
+     * An interceptor should provide two methods;
+     * - an "intercepts" method takes a class name and returns boolean
+     *   (true if the interceptor want to intercept)
+     * - a "get" method which returns the object, given it's class name
+     */
+    public static function registerInterceptor($interceptor) {
+        self::$interceptors[] = $interceptor;
+    }
 }