Picture those "bar ends" that you'll find on mountain bikes. (and others, I suppose)
Those make a fine mirror mount.
You simply drill through it, front to back. I used a couple of motorcycle mirrors, about 3" round. You pass the bolt from a seat post clamp through the hole you drilled and the flanges from the clamp will hold on to the mirrors arm.
I mounted the bar ends just inside my grips and levers. The bar end gets everything above your hands and the mirrors arm can be tilted so that the mirror sits outside of your wrists.
You'll need the actual mirrors, of course. But stainless steel bicycle mirrors can be found online. And I imagine motorcycle mirrors could be found at a garage/motorcycle junkyard.