If you go into the key bindings, there is a section for you to map your own key bindings to custom controls. I assume here you can have your stance adjust and up/down bound to a single key to accomplish what you're wanting to do. Otherwise, I would just say get used to pressing multiple keys.

If applicable, just have stance adjust bound to a mouse key, like Mouse 4 or 5, or higher if you have the available buttons on your mouse.