I was involved in a study many years ago looking at just that. We took some inexperienced people who had a mix of flying experience (including a couple of PPLs) and got a type rated pilot to talk them down on a fairly realistic B747 PC simulator - one used by the industry for training and not MS Flight Sim.
There's two elements to this. First, the person in the seat has to find the correct function to activate and second, the pilot doing the talk-down has to express himself correctly in order for that to be achieved. This one is the most important for if the seat occupant gets the wrong selection, then there is problems ahead as the talk-down pilot now will not know which mode the auto-flight system is in - unless he gets the occupant to confirm every mode through the Flight Mode Annunciations - which isn't easy.
Interestingly, the experience of the person in the pilot seat made little difference. It was the quality of the talk-down which was the deciding factor. In fact, some experience could be a bad thing as one of the PPLs though that it would be best to take out the Autopilot on the approach as he had the (over)confidence to land it himself. It's safe to say that if this happens - it's game over. An auto-land is a must.
I recall there was about a 50% success rate.