square group brackets

[Dewdman42]

Hi everyone.  I can't seem to figure out how to make a square looking group
bracket.  I'm trying to make the kind of staffgroup bracket that looks like
a solid back rectangle laying just to the left of the starting barline. 
Like this(see attachment):

http://www.nabble.com/file/p11491788/ScreenHunter_01%2BJul.%2B08%2B12.17.jpg 

Is there a straightforward way to get these in Lilypond?  I also can't seem
to figure out how to put a staff group bracket around only a single staff. 
When it try it, it seems to just leave off the bracket.  Here is the general
grouping syntax I am using:

        \new StaffGroup
        <<
          \new Staff {
                \clef treble
                \set Staff.instrumentName = "Clarinet"
                <<
                  \meterMap
                  \clarinetOnePart
                >>
          }
          \new Staff {
                \clef treble
                \set Staff.instrumentName = "Clarinet"
                <<
                  \meterMap
                  \clarinetTwoPart
                >>
          }
        >>
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