Flatphone Shoulder Rest

People have been holding phones (the mouthpiece/earpiece part) with their shoulders for so long that special tools were made to make the holding more comfortable. See link.

Well, why isn't there such a thing for today's flat phones? We don't want the shoulder rest to be permanently attached to the phone, but it could be attached to a phone-holder. Slide the phone into the holder, then rest it on the shoulder.

I'm guessing the main problem is, where do you put the shoulder rest when you are doing something else with the phone? Short of permanently attaching the rest to the shoulder (the shirt or blouse or jacket or...), perhaps a modification to the back side of the phone itself could work. Imagine a simple rod/handle, that was attached to a tiny air pump. Use it to inflate a balloon-type membrane attached to the back of the phone. When done having the phone on the shoulder, press a valve- button (normally held closed with a spring) to let the air out.