Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.9) Gecko/20100317 Thunderbird/3.0.4
Why not just change the page size to something larger than A4 in the
paper section (don't change anything else) and then just use the
reducing capabilities of the printer driver to shrink the output to A4.
I have one score that occupies 17 pages when the ly file is set to
output to A4. I changed A4 to A3 and it outputs to 8 pages, and I can
get that 8 pages printed on A4 by telling the printer driver to shrink
pages to fit.