Index: wp-config-sample.php
===================================================================
--- wp-config-sample.php	(revision 7010)
+++ wp-config-sample.php	(working copy)
@@ -21,6 +21,10 @@
 // to enable German language support.
 define ('WPLANG', '');
 
+// WordPress wil store temporary files in this directory. Using an empty
+// directory is recommended.
+define('WPTEMPDIR', '/tmp');
+
 /* That's all, stop editing! Happy blogging. */
 
 define('ABSPATH', dirname(__FILE__).'/');
Index: wp-admin/includes/file.php
===================================================================
--- wp-admin/includes/file.php	(revision 7010)
+++ wp-admin/includes/file.php	(working copy)
@@ -182,7 +182,7 @@
 	if( ! $url )
 		return false;
 
-	$tmpfname = tempnam('/tmp', 'wpupdate');
+	$tmpfname = tempnam(WPTEMPDIR, 'wpupdate');
 	if( ! $tmpfname )
 		return false;
 
@@ -288,7 +288,7 @@
 }
 
 function get_filesystem_method() {
-	$tempFile = tempnam('/tmp', 'WPU');
+	$tempFile = tempnam(WPTEMPDIR, 'WPU');
 
 	if ( getmyuid() == fileowner($tempFile) ) {
 		unlink($tempFile);