Wow, it only took me 10 year to solve this one proper...

Subclass the WM_WINDOWPOSCHANGING message. The lParam is a WINDOWPOS. In vb6, you need to use RtlMoveMemory api function to copy the lParam to an empty WINDOWPOS variable.

Set the hWndInsertAfter field to HWND_BOTTOM and copy the structure back to the lParam.

In .Net (where I solved this problem), override the wndproc method. Look for the WINDOWPOSCHANGING message.

vb Code:
  1. Dim memloc As IntPtr = m.LParam

  2. Dim pos As WINDOWPOS = m.GetLParam(GetType(WINDOWPOS))

  3.  
  4. pos.hWndInsertAfter = HWND_BOTTOM

  5.  
  6. Marshal.StructureToPtr(pos, memloc, True)