In another question, Harald showed how to make vertical leaders. Armed with this knowledge, I set sail to answer another question, but as I've tried to put such leaders into a page with other material as well, the leaderfill always takes up the whole page.
Is there a general way to typeset something onto a page, which then would be handled by TeX as if nothing had been typeset at all (i.e., it wouldn't take any kind of space away from other material)?
Example:
\newbox\needlebox\setbox\needlebox=\vbox{\hsize=2em$\cdot$}
\def\needlefill{\cleaders\copy\needlebox\vskip0pt plus 1fill}
\llap{\hbox to 2em{\vbox to\vsize{\hsize=2em\needlefill}}} Blah
\bye
(The "Blah" goes to second page)