[Crssi]

I have Windows... its in the registry... but you can do it very easy with Advanced MCE Remote Mapper Tool
Remember to run it with elevated (admin) and after setup to reboot.

I have assigned some special MCE sequence (yellow button), that I dont use, to sleep (my choice, it could be also poweroff) in win and this same sequence as poweroff FIX in the harmony power settings for this device.

Yellow button:
I dont use yellow sequence for anything else, since I have assigned some other key to yellow button on harmony, which is then binded to subtitles functions in Kodi.
So when I press yelllow button on harmony it opens me subtitles timeshift.

UPDATE: I dont use OpenElec at this time, so I dont know ho to configure OE for it.

Another UPDATE:
I have also put STOP playing in the power off sequence.
Why? Because if you turn off NUC/kodi when playing some file, then kodi does not remmember where it stopped.
So power off sequence in my case first tell kodi stop playing whathewer you play or not at this moment, and the next squence is power off (yellow as a sleep as my choice)