--- settings.php 2008-06-11 22:23:18.000000000 +0900
+++ settings.php 2008-06-11 16:19:25.000000000 +0900
@@ -163,3 +163,17 @@
 #   'anonymous' => 'Visitor',
 # );
 
+
+/**
+ * Backport of Drupal 6.x custom_url_rewrite_outbound
+ * Used by subdomain module to rewrite outgoing URLs
+ */
+function custom_url_rewrite_outbound(&$path, &$query, &$fragment, &$absolute, &$base_url, $original_path) {
+
+  if (module_exists('subdomain')) {
+    // extract subdomain from $path if present and add to $base_url
+    subdomain_url_rewrite($path, $base_url, $absolute);
+  }
+
+  // You can perform additional URL manipulations here if you need to
+}