I completely agree with Dan Winterland, there would be no problem talking somebody through an autoland. I don't think that any PPL could just sit in a 747, kick out the autopilot and successfully manage to land it unless they’ve flown larger things in a previous life (RAF etc). The inertia and the pitch power couple would probably lead to it being over-controlled, completely unstable they’d most likely miss the runway and the speed control would probably be all over the place as their scan is unlikely to be quick enough in an unfamiliar aircraft.
Secondly if you were in an unfamiliar place would you know ILS frequencies or have any idea where you are and which airfields are suitable? What about high terrain? I think you'd need to establish comms in order to get some idea of which way to go.
Now cabin crew can access the cockpit in an emergency without the need for a crash axe, and the chances are they would have been showed how to select 121.5 on the radio and make a call. With a type rated pilot talking to the cabin crew member I feel certain that the aircraft could be configured for an autoland as Dan has shown. Personally I’d just get them to use heading select and level change to get them to the platform altitude on a very very long final, then tune the NAV boxes, put in the VREF (or just grab some figures from the QRH and forget the FMC), configure the aircraft for an autoland and once on the ground get them to shut down the engines.
If you had a flight simmer who has spent sufficient time with PMDG 747 or PS1.3 then they would have very little difficulty setting up the aircraft for an autoland once the cabin crew had got them into the cockpit and got the communications established. It would probably be easier to talk someone down who knew their way around FMC, MCP, ND and PFD rather than trying to get the information out of cabin crew who wouldn’t know where to look. I speak from experience on the subject of flight simmers as I used PMDG's 737 prior to getting type rated on the NG and it taught me my way around the FMC, MCP, ND enough to do an autoland, similarly I'd used PSS's A320 add-on prior to doing my MCC in the A320 and I could also set that up for an autoland prior to setting foot in the real sim.
So once I’d got my PPL and prior to getting my fATPL I reckon I could have done an autoland on a 737NG, 747-400 and the FBW Airbus family IF somebody had pointed me towards the airfield and giving me the frequencies
Could I have worked out how to use the radio? Probably but there are a lot of buttons on the ACP. I think if I’d of disengaged the autopilot trying to find the PTT I would have known that the way out was to push one of the CMD / AP buttons.
Could I have hand flown them to a successful landing?? Not a chance, I’m sure we’d have ended up in a burning heap.