Vertical spacing on final page of score

[Graham King]

I'm having a bit of a struggle with the spacing of systems on the final page of a 12-page score.  With 
\paper { ragged-last-bottom = ##t }
the final page has three systems crowded together, followed by a sea of whitespace, then the copyright line.  But with
\paper { ragged-last-bottom = ##f }
the spacing between systems is reasonable but the final system is too close to the copyright line.

I've tried various things, including:

• changing the copyright line to \markup { \center-column { " " \vspace #10 "some text" }}
• changing \paper { system-system-spacing #'basic-distance = #29 }