He really should just choose a major that he would be happy in. From the website:
The Imagineering organization encompasses more than 140 diverse disciplines, including writers, model-makers, computer animators, artists, engineers, sculptors, filmmakers, scientists, programmers, special effects designers, architects, master planning, creative development, production and Walt Disney Imagineering Research and Development.
So rather than choosing a major that will give him the best shot at being an Imagineer, he should just go with one he will like. There isn't much point in studying engineering just to be an Imagineer if he HATES engineering. They need a LOT of different professions.