[texhax] \vskip

[Pierre MacKay]

Now I see that the problem is to get to the top of the same page.  

I do this with transparent overlays.  I set the material with varying depth
in a box which is then declared to have zero height and width, so that when
I am finished, I am still back where I started.  It works for several
multicolumn environments that look rather like sidebars, because they are
use fonts and leadings that are not used elsewhere in the page.

Getting it started is a bit of a pain, but it has been so useful that I
have entire formats based on transparent overlays.  Unless you are generating 
the content of the sidebar as you write the page, it should work.  I wonder whether 
it might also be possible to do something with a zero height insert. 

Pierre MacKay