Hold the post button ?

Up on the center.. where once was the Amethyst logo

On the left menu, make an entry called STREAMS where all streams from follow are shown, and where the user can additionally click a button written "Start my stream"

+1 for side menu or expandable compose button. Or Add a tab to the verified media page for image/video and one for streams adding a start stream button like the compose on that for doing a stream over watching them.