Height and vertical alignment of first system on first page

[Jonathan Scholbach]

Hi Ponders,

I have a score with an odd number of systems. Each page has two systems
(it's an eight-voiced Choirstaff), the first page gets one system (and
the title-section) - fine.

Lilypond stretches the first system vertically to make it fill the whole
first page. I would like this system to have the height of the other
systems in the score and to be placed in the (vertical) center of the
first page. Can you tell me how to do that? I have tried to cheat
lilypond by adding some \vspace in the \title of the \header - that
reduces the stretch of the system, but still lets it stretch to the
bottom of the page - I would like the system to be right in the middle
of the first page.

Your help is appreciated,

Jonathan