Index: wp-includes/template.php
===================================================================
--- wp-includes/template.php	(revision 21103)
+++ wp-includes/template.php	(working copy)
@@ -386,6 +386,8 @@
 	if ( is_array( $wp_query->query_vars ) )
 		extract( $wp_query->query_vars, EXTR_SKIP );
 
+	$_template_file = apply_filters( 'template_file', $_template_file, $require_once );
+
 	if ( $require_once )
 		require_once( $_template_file );
 	else