Show Fullscreen Portrait Layout with Miracast
I am sorry to have to tell you this, but this is not possible.

The OS outputs the data to the screen, and the screen follows this. When the device is in portrait mode, that is what the device outputs - as the screen has wide space, it fills it with black bars.

This is the same for the iPad's (I know, I hate them as well) with their screen connectors - if the iPad is in portrait mode, then the screen sits in the middle of the screen.