centering instrument name between staves

[David Bobroff]

I'm trying to center an instrument name between two staves in a 
StaffGroup.  I looked for something in the docs and the LSR that was 
similar and didn't find what I was looking for.  The closest thing is a 
piano staff.  I tried setting the systemStartDelimiter to 
systemStartBracket but then I got the curly brace AND the bracket.

To be as clear as possible; I want to position this like the word 
"Piano" would be placed on a PianoStaff but with a square bracket rather 
than the piano curly brace.

Thanks,

David