Different staff sizes

[Johannes Eva]

Hi everybody!

I'm new to this list, though I have been using and hugely appreciating 
Lilypond for many years now. I am writing a book of little pieces for 
violin beginners, free to use and copy of course :-) I'll set up a 
website for it in the next months.

I am now blocked by what I consider a Lilypond limitation, but maybe I 
just couldn't figure out how to do what I want. I'd like to have my 
little pieces in one big pdf file. The problem is: I need different 
staff sizes for different pieces and "chapters" of the book.

#(set-global-staff-size 14) does only work for books, but not for 
\bookparts!

Using layout-set-staff-size makes only the font bigger (if I'm right), 
but not the lines, so that following solution does not work:

\score{
  \relative c' { c4 d e f g1 }
  \layout {
    #(layout-set-staff-size 15)
  }
}

\score{
  \relative c' { c4 d e f g1 }
  \layout {
    #(layout-set-staff-size 30)
  }
}

According to Google, this seems to be a wide-known problem.

Is there any trick or tweak to scale the staves and lines to 
layout-set-staff-size? Or any other way to have different staff sizes in 
one document with Lilypond?

Does this bug report shows that there is no hope?
http://code.google.com/p/lilypond/issues/detail?id=216

Is an ugly trick excluded, a way to go around the problem?

Thank you for your time, greetings from Nürnberg, Germany,
Johannes