Login Script for deleting contents of /private/var/folders
It's a simple way. You can use the getconf DARWIN_USER_CACHE_DIR command to get the per-user temporary files and caches directory. and remove it. edit the '/etc/profile' file, add the following codes in it(not test yet): 

userTempDir=`/usr/bin/getconf DARWIN_USER_CACHE_DIR`
rm -fr $userTempDir*