Index: aggregation.module
===================================================================
--- aggregation.module	(revision 31037)
+++ aggregation.module	(working copy)
@@ -1332,7 +1332,16 @@
 
 	$feed_xml = aggregation_get_XML($data, $feed);
 
-	require_once(drupal_get_path('module', 'aggregation')."/feed_handlers/$handler_name.inc");
+  $theme_path = drupal_get_path('theme', variable_get('theme_default', NULL));
+  $possible = file_scan_directory($theme_path, "$handler_name.inc");
+  if (!empty($possible)) {
+    // @TODO: should we warn if there are multiple versions of the same file?  
+    $file = array_shift($possible);
+    require_once($file->filename);
+  }
+  else {
+    require_once(drupal_get_path('module', 'aggregation')."/feed_handlers/$handler_name.inc");
+  }
 
 	try {
 	call_user_func_array('_aggregation_'.$handler_name.'_parse', array($feed_xml, $feed));