Assuming you have a window which has a panel on it and a background...
1. Add a child game object to your first panel, put a UIPanel on it.
2. Bring it forward (-Z transform).
3. Set up clipping properties you want to have.
4. Add children to this new panel that will be clipped.
5. Add a UIDraggablePanel script to this new panel, set it up how you want it (scale 0, 1, 0 to drag vertically for example).
6. Add a collider to the background sprite (that's a child of your original first panel).
7. Add a UIDragPanel script to the same sprite.
8. Reference your UIDraggablePanel on your UIDragPanel script from step 7.
That's it.