Basically what he is proposing to do is raise one wing panel up 5" with the jig while the other panel is laying flat on the board, glue the sheeting in place on one panel (not sure if he is gluing the sheeting on the raised panel or the panel laying flat). Then place the jig at the reverse end of the wing and do the same.

Is it possible that if he applies the sheeting in place on the raised panel, and then reverse sides and do the same to the opposite panel, will the washout still be built in?