Single note analysis brackets?

[Hugo Flordal]

I'd like to use the Horizontal_bracket_engraver to indicate single notes, but it
seems analysis brackets can only be used over multiple notes. I'm attempting to
write 
  c8\startGroup\stopGroup
but this isn't working. Is it possible to get around this somehow? Perhaps by
adding a dummy note with zero width somewhere? All my experiments and solution
searches have failed...
  I also tried using the Ligature_bracket_engraver, but it does not appear to be
very stable and I can't find a way of tweaking it into producing horizontal
brackets at a fixed height.

It would be nice if analysis brackets could be generalised so that they could
replace the Ligature_bracket_engraver completely... (And perhaps use the \[ \]
notation as well...)