Comment 468 for bug 59695

ethanay: have you tried adding your script to /etc/acpi directories per the ubuntuforums post?
http://ubuntuforums.org/showpost.php?p=3675960&postcount=26

Also, you should be able to run "sudo hdparm -B 254 /dev/sda" on startup by adding it to System > Preferences > Sessions.