system start delimiter for one staff

[liang seng]

Hi, I'm using Lilypond 2.7.27 for Windows 98. I would like to know if we can 
force a system start delimiter (a bracket) to appear before a StaffGroup or 
ChoirStaff that has only one staff.
Here is an example:
\version "2.7.27"

{
\new StaffGroup { <<
\new Staff {  R1  }
>> } }

Here, I want the bracket to appear before the staff even though there is 
only one staff in the StaffGroup. How can I force the bracket to appear? 
This is because if I recall correctly, the stable version 2.6.3 allows 
brackets to appear in StaffGroups or ChoirGroups which contain only one 
staff.
Thank you.