I would think a penlight or something similar would be fairly unobtrusive. Honestly, I'd probably never even notice.
I'm curious as to how many of the people that do find this distracting have children? That's not meant as an inflammatory question, just an honest question?
I mean, realistically, there are tons of distractions on any given ride at WDW. I would take a boatride with a youngster holding a small penlight over a boatride full of loud, obnoxious teenagers anyday.
Pick your battles, I say.