aleatoric box / frameEngraver

[Karol Majewski]

Hi again. This time i'm trying to modify frameEngraver written by David 
Nalesnik (Big thanks). I'm using 2.16.2 version of LilyPond and 
frameEngraver8.ly, which you can find here:

http://lilypond.1069038.n5.nabble.com/attachment/139396/0/frameEngraver8.ly

So, what I'm trying to achieve is to replace the frame with repeat signs, so 
that you have:

|: music :|----------->

This is so called indipendent repetition and it's very common in contemporary 
music.

I have no idea how to do this. Any Any ideas would be greatly appreciated...