I had radio contact with someone giving instructions, then I would like to think there was something of a fighting chance!
Well it wouldn't hurt, but there's still going to be a world of difference between being coached/prompted by someone sat next to you (as in the sim) and who could see directly what you were seeing in the way of airspeed, altitude, etc, vs. the real world where you're probably going to have to tell your "helper" all the numbers via radio.... That would up your workload phenomenally and increase the level of difficulty by an order of magnitude. Having Mode S (which very basically allows ATC to "see" some things in the flight deck) may help on that front but not everywhere/every aircraft has got it and your "instructor" may not have time to get to a suitably equipped console before your fuel runs out.......
I've only seen the aforementioned Mythbusters episode once but, and I may be wrong, I got the impression the instructor, sat outside the sim, had a full set of the Flight Deck displays available to him and was using these to help out Adam/Jamie on their second, "assisted" run. Anybody with access to the episode know if that was indeed the case?