[LittleTalker]

I achieved more or less the same result using acrobat, but without this autopagex plugin. (note I said acrobat and not adobe reader).
Here's what I did with an A4, 12pt font and generous margins document:
I cropped the whitespace, and then I printed to a new file using the adobe printer, setting the page size to 120x150. I configured the print setup to 'tile all pages' and reduce the zoom level to somewehere near 80%, so it doesn't split every page in four.
I also set a 5mm overlap (the amount of the bottom of the first half that gets repeated at the top of the second half), which works well for a 12pt font.
The effect is that Acrobat automatically prints to landscape and splits the pages in half, repeating the parts that overlap to the specified parameter[funny: I set the printer to landscape and the result were pages upside down... someone said something about left handed use...]. So you get a new PDF document with some margins on the sides, which you can use to insert a page number.
I played around using the adobe printer along with acrobat, you can achieve some decent results. I am yet to try this, but I plan to print to pages slightly smaller in height than 150mm, then add top and bottom margins using the crop tool. That way the split pages will look much better.
Well, I guess the results are good 'cause the damn thing just isn't here yet. I think the results I got should be quite readable on the iLiad. I can't upload the files since these are copyrighted books.