bracketed passages

[Monk Panteleimon]

Dear Lilypond users,

I would like to place brackets around passages of music -- not around 
arpeggiated chords or notes in chords or anything like that, but a 
right-pointing bracket at the beginning of a passage, spanning the whole 
staff or system, and likewise a left-pointing one at the end of the passage. 
This is to indicate that the passage in question ( a long melisma called a 
"fita") can be either sung or omitted at the discretion of a chanter or 
director. There is a not-very-attractive example of this kind of thing at the 
end of the 7th system in the piece of music posted here:

http://www.rocmconference.org/music/V4-12_Lord-I-have-cried_Both-now.pdf

Whoever engraved this piece in the early 20th c. used parentheses, but I would 
rather used something that looks close to a SystemStartBracket, but maybe 
thinner, and of course reversible for the close of the fita. 
* I have already tried doing this with markups, * using both parentheses and 
brackets. The problem with this method (besides all the trial-and-error 
tweaking of sizes and offsets) is that by the time the things are big enough 
to embrace the system, they are awfully fat and unsightly. 
Any suggestions will be greatly appreciated.

Fr. P