Sandboxing prl_disp_service to prevent disk waking
Yay, I managed to sandbox prl_disp_service \o/

I put a file named prl_disp_service.sb into /Library/Sandbox/Profiles denying ioctl on disk1 (the harddisk I wanted to prevent from waking):

(version 1)
(allow default)
(debug deny)
(import "system.sb")
(deny file-read* file-ioctl
    (regex "/dev/disk1*"))


And edited /Library/Parallels/Parallels Service.app/Contents/Resources/ParallelsDispatcherService:  

sandbox-exec -f /Library/Sandbox/Profiles/prl_disp_service.sb "${ParallelsDispatcherService}" -e --logfile "${LogFile}" --pidfile "${PidFile}" &gt;/dev/null 2&gt;&amp;1 &amp;