His full weight was already on the plane, so as long as his movements are smooth enough, he won't dislodge it any further. He should be careful climbing over the lip - the rusty edges are pretty sharp, and that's how you get tetanus!

If he chooses to climb down inside: The closest thing to stand on once he's on the inside of the lip is probably the backs of the second row of seats, about five feet below the lip.

How does he proceed?