Index: wp-admin/includes/file.php
===================================================================
--- wp-admin/includes/file.php	(revision 6979)
+++ wp-admin/includes/file.php	(working copy)
@@ -182,7 +200,7 @@
 	if( ! $url )
 		return false;
 
-	$tmpfname = tempnam('/tmp', 'wpupdate');
+	$tmpfname = tempnam(CACHEDIR, 'wpdownload');
 	if( ! $tmpfname )
 		return false;
 
@@ -288,7 +306,7 @@
 }
 
 function get_filesystem_method() {
-	$tempFile = tempnam('/tmp', 'WPU');
+	$tempFile = tempnam(CACHEDIR, 'checkfile');
 
 	if ( getmyuid() == fileowner($tempFile) ) {
 		unlink($tempFile);
Index: wp-settings.php
===================================================================
--- wp-settings.php	(revision 6979)
+++ wp-settings.php	(working copy)
@@ -323,6 +323,14 @@
  */
 if ( !defined('COOKIE_DOMAIN') )
 	define('COOKIE_DOMAIN', false);
+	
+/**
+ * Cache directory for WordPress, Defined as Absolute to allow for non-WP directories
+ * It is possible to define this in wp-config.php
+ * @since 2.5.0
+ */
+if( ! defined('CACHEDIR') )
+	define('CACHEDIR', ABSPATH . 'wp-content/tmp/');
 
 require (ABSPATH . WPINC . '/vars.php');