Phone controller for Portrait orientation

In my search for the ultimate retro gaming machine I’ve been surprised by the limited options when it comes to controllers for iOS and android. While there are plenty of controllers that you can clip your phone onto in landscape orientation, I haven’t seen any that are designed to play in portrait mode. I see several benefits to a clip on controller for portrait mode. Pinball games, Tetris, and DS games all play best in portrait mode. Plus, a portrait mode controller would be close to the original gameboy in terms of form-factor.

Anyone else looking for something like this? Have I missed a product that’s out there? Maybe once I get a 3D printer I can cannibalize a Bluetooth controller and experiment.