Customization Dialog

The following routine can be used to simulate the execution of any control based on the ID of that control:

Public Sub ExecuteCommandBarControl(ByRef CommandBars As CommandBars, ByVal ID As Long)
  Dim TempBar As CommandBar, Control As CommandBarControl
  If CommandBars Is Nothing Then Exit Sub
  Set TempBar = CommandBars.Add("Temp", xtpBarPopup)
  Set Control = TempBar.Controls.Add(xtpControlButton, ID, "Temporary")
  Control.Execute
End Sub

Just pass a reference to your CommandBars object and the ID to execute.  The trick here is that you need the ID of the 'Customize' menu option.  I don't know this off the top of my head, but it's easy enough to find out.  Just place a debug message in the 'Update' event of CommandBars to output the Caption and ID of the control being updated.  When you drop down the menu that has the 'Customize' option, it'll trigger the 'Update' event and you'll see the proper ID value in the debug message.

Hope this helps lead you in the right direction.  This was the best hack I could come up with since they didn't provide a basic method for this.  Enjoy!