Could this be it? the
Comtek Wireless Cueing System:
I was browsing one of my favorite gadget sites
GIZMODO and found this ...
To quote from GIZMODO:
"They aren't exactly new, nor are they particularly hot, but they have been big news as of late due to the possibility (real or imagined) that George W. Bush received either coaching or direct answers through such a system at the Presidential debates."
It looks pretty tiny, all he'd have to do is wear the loop around his neck and the ear piece would be invisible.
It really is pretty tiny - the thing you see sticking out in the middle is the open battery door, so it is even smaller than it looks here.
This could do it, and GIZMODO says it's been around for a while.
Things that make you go "Hmm"...