Such things do exist, but they're outrageously expensive at the moment. (As are most accessibility solutions for people with disabilities... )
http://orin.com/access/pagebot/
With an infrared touch screen you could tap the screen gently with a knitting needle or a waft of yarn. (Or even a toe, if you're really dexterous!) I don't think the inanimate bits will work with the Paperwhite's capacitative touch screen, though; you'd need a special stylus and that would involve putting something down.