In fact, overlaying the scrolling view with the AppBarLayout is an included feature of the Android Design Support Library: you can use the app:behavior_overlapTop attribute on your NestedScrollView (or any View using ScrollingViewBehavior) to set the overlap amount:

<android.support.v4.widget.NestedScrollView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    app:behavior_overlapTop="64dp">

Note that app:behavior_overlapTop only works on views that have the app:layout_behavior="@string/appbar_scrolling_view_behavior" as it is the Behavior that is using the attribute (not the View or the Parent ViewGroup, as attributes usually apply to), hence the behavior_ prefix.

Or set it programmatically via setOverlayTop():

NestedScrollView scrollView = ...
CoordinatorLayout.LayoutParams params = 
    (CoordinatorLayout.LayoutParams) scrollView.getLayoutParams();
AppBarLayout.ScrollingViewBehavior behavior =
    (AppBarLayout.ScrollingViewBehavior) params.getBehavior();
behavior.setOverlayTop(128); // Note: in pixels

In addition to the accepted answer, call setTitleEnabled(false) on your CollapsingToolbarLayout to make the title stay fixed at the top as in the example.

Like this:

CollapsingToolbarLayout.setTitleEnabled(false);

or by adding it in xml like this:

app:titleEnabled="false"

Otherwise the title could disappear behind the overlapping content, unless of course, that's the behaviour you want.