9-16 feels like a dirty word but sometimes it's a necessary evil. And yes, you could crop from the middle but you could also get the most out of your sensor and mount the camera sideways. Enter the L-Shaped cheese plate. 
 
Mount a variety of cameras, plates, and accessories with this L-Shaped Cheese Plate Mounting Platform. This two-piece cheese plate can be used separately or mounted to form an L-shaped mounting bracket. Each piece features twenty 3/8"-16 and sixteen 1/4"-20 threaded mounting holes, as well as four 1/4" mounting slots for flexibility in mounting. Built-in angle brackets keep the plates solidly together when mounted as an L-shaped bracket.
 
So go on, embrace that vertical shot!