How can i remove the label indentation from a frame?

[Jef Driesen <jefdriesen hotmail com>]

For grouping related items in a dialog, I'm wanted to use a HIG style 
frame like this:

GtkFrame (bold label, no visible border)
   GtkAlignment (12px padding left, 6px padding top)
      <child widget>

But the label of the frame is indented a few pixels. Since the frame has 
no borders, this indentation appears as extra left padding between the 
frame and its parent widget. Also the 12px padding of the Alignment 
seems to be reduced by this indentation. Is there a way to remove this 
indentation? Or is the only solution not using a frame, like this:

GtkVBox
   GtkLabel (bold label)
   GtkAlignment (12px padding left, 6px padding top)
      <child widget>

If this is the only way, why does the GtkFrame widget still exist? 
Because I would find it rather strange that it's nearly impossible to 
obtain the preferred style [1,2] with the widget that is designed for 
this type of layout.

I found a related bugreport [3] where the (removal of the) indentation 
is mentioned, but as far as I can tell it was never implemented.

[1] http://developer.gnome.org/projects/gup/hig/2.0/controls-frames.html
[2] 
http://gnomejournal.org/article/44/three-simple-tips-for-interface-design-you-should-know
[3] http://bugzilla.gnome.org/show_bug.cgi?id=96374 (comment 7 and 12)