You need to be two to do this but you can start a google on air using a computer, have the person using a mobile join the conversation. Then simply click on them so they are fullscreen, you are now broadcasting live from a mobile. I am hoping that the feature will soon come to the mobile app but in the meantime this is a great work around.
I did not make a video because Ronnie Bincer who has a youtube channel full of tips had already made a good example of what I am talking about.