I would try to plan rides and activities that emphasize other senses like hearing and touch. For example, "Sounds Dangerous" at MGM Studios is very entertaining. It's mostly in the dark and the entertainment comes from what you hear. If your cousin likes roller coasters, Space Mountain is fun and the emphasis is on the ride itself more than on what you see as you're whirling around in the dark. Mission Space might also be a good choice as the physical experience is great even without the visuals. Same for Test Track.
These are a few I could think of off the top of my head.
Hope you have a wonderful time.