Using headers inside of a score

[Jakub Pavlík]

Hi,

it would be very useful for me to be able to access score headers inside of the 
score, like this:

\score {
  \relative c' {
    \set Staff.instrumentName = \markup {
      \fromproperty #'header:piece
    }
    a a a
  }
  \header {
    piece = "Great Piece"
  }
}

But it doesn't work. Is there any way to do this (take some score header and 
set it as instrument name)?

Thanks, Jakub