With a slightly different aspect, there's an article in this months UK Pilot magazine discussing whether a PPL could land a 747 in an emergency. The vote was no.
On this subject, ie with training is it possible, I'm not sure how this would work as the 747 is certified as a two crew aeroplane, so you'd need at least 2 PPL's. Assuming it's privately owned, the CAA would be interested in all the other arrangements like standard operating procedures etc.
I reckon it's a no-goer.