Serious question -
I've seen it in movies, but I've doubted it's possibility.
What are the chances that a second plane with radar blocking equipment engaged the 777? Make a connection. Send a few trained guys on board. Commandeer plane.
The latest I'm reading is that the plane flew quite a ways off track as if it were being controlled by a human. It means one of three things: one of the pilots did it, an on board trained hijacker did it, or an outside party did it.
Unless they've kept information about the passengers secret, there aren't any signs that any passenger could have been capable of flying the plane.