Using google cam to make horizontal 180-degree fisheye pics

On my Nexus 5, I'd like to use the google camera in panorama mode to make a 180-degree fisheye photo. I want to do this holding my phone in such a way that the lens is looking UPWARDS (towards the sky). In other words, my zenith should be in the middle of the final processed picture. Unfortunately, I can only create fisheyes when I hold the phone in an upright position, i.e. when it is aligned to the horizon. This means that by the end of the whole process, I am going to have a final image showing half terrain, half sky. When I hold my phone horizontally,thus looking upwards, before starting the capturing process an arrow appears that forces me to put it in a vertical position - aligned with the horizon - before it creates the first pic. See here https://drive.google.com/file/d/0B4Xl49qe9PWbYk5lcXA2czY4aDg/view?usp=sharing The reason why I want to do this is because I'd like to put this picture on a planetarium dome. These domes represent the sky above us and therefore show mostly sky and not terrain. Here's an example pic of what I want to create: Any ideas?