It appears that http://codeversed.com/expandable-notifications-android/ has the answer in the Custom View at the end.
So what if the rich notification styles don’t provide you with the layout you need? Easy, just create your own layout and pass it to the builder. One little fact to retain is that notifications use remote views, which means you need to create a layout using a RemoteView. Below is exactly how you would need to create this custom RemoteView.
notification.bigContentView = expandedView;