Unreal Engine dynamic assets

I'm using the Unreal Engine runtime to create a button that can support dynamic text and a button mapping icon. For example, I have a confirm button and would like to display either the enter key if a keyboard is being used or a gamepad start button if a controller is being used.

Setting text at runtime is easy enough but I don't see a way to set the input mapping button image at runtime. The features page calls out being able to set these at runtime so if somebody could let me know if this is just not possible in the Unreal runtime or if it is and could point me in the right direction I'd appreciate it.