I posted this a little while ago on another topic, here it is again...
"I finally got around to trying out my idea about "learning" the reboot command from the AppleTV remote and IT WORKS. The dual button press (of - and Menu) actually sends a discrete IR code after holding for 6 seconds. I captured/learned this command w/ my harmony remote. I just pointed the AppleTV remote away from the harmony remote at first and then pointed it back at the learning port after a second, in time to capture the AppleTV reboot signal. It took two tries but I got it.
I've tested it now and can do a one button reboot whenever needed from my harmony remote."