I'm trying to do the same thing.
I managed to hide my DockablePane at startup by calling the "dockingManager.ToggleAutoHide(myPane)" method when my window is created.
The problem is that the "button" that shows my DockablePane on mouse over is displayed on the left side of my window whereas I would like it to be on the bottom of my window.
Does anyone know how I can achieve this ?
Thanks a lot.