Is there a reason you can't just prop the Kindle up vertically? I mean, somewhere lower, where you don't need to see THROUGH it. Though I guess that's the whole point of a "heads up" display, is to have it in your view-field but not interrupt your view, so you want to see through it. So, probably never mind my question.
But still --- mounting a kindle vertically, somewhere lower, sounds easier! It just wouldn't be a "heads up" thing.