Windows Advanced User Interface (MDI Tabbed Group)

I would like to be able to create an MDI mock interface that extends the MBO Tabbed Groups behavior as follows. Inside the pane for a split tab group, I would like to create a group of nested tabs with opposite directional alignment. For example, given the top level horizontal splitting, I would like to create a vertically split tab group in the first panel. This appears to require reworking CMDIFrameWndEx and related classes.

Tabbed group layout - attractive user experience. It's a shame not available in major browsers. Am I correct in assuming that its best support is in the Visual C ++ Feature Pack?