I've actually found several tmp directories (writable by everyone): /home/virtual/site22/fst/tmp /home/virtual/site22/fst/var/tmp
I'm not permissioned to write to /var/www/
I wonder if there is somewhere I can tell the mediawiki installer to use on of those tmp directories.
Try adding this to LocalSettings.php:
putenv("TMP=/home/virtual/site22/fst/tmp");