Book building help

[Mark Probert]

Hi, again.

The task I'm attempting is to create an equivalent of a fake book. I'm 
creating a tune in concert (C) and then collating it with other tunes 
using \bookpart. That works fine for the most part. The problem is when 
I want to have the fake book transposed (say for Ees). I end up with a 
structure like:

%%%
\include "tune_a.ily"
\include "tune_b.ily"

\book {
  \bookpart {
    \score {
       \transpose c a { \tune_a }
    }
  \bookpart {
    \score {
       \transpose c a { \tune_b }
    }
   % etc.
  }
}
%%--

Which is a pain if I have a lot of tunes, I'm repeating this for each 
key (for jazz it is common to have C, Bes, and Ees versions) and a mess 
if I want to reorder tunes, make edits, and so on. 

Is there a better and cleaner way to approach this problem?

TIA .. mark.