It is kind of a sideways way of doing it, but you can use a PDF creator software to break the file up in to smaller chunks.
I use PDFCreator, an open source PDF writer that installs as a printer, available here:
http://sourceforge.net/projects/pdfcreator/
Open the document in Acrobat Reader, Choose "Print" and select the "PDFCreator" printer, and it will create a new PDF file. Just print it twice, splitting it in the middle. (In other words, if it is 500 pages, job 1 will be pages 1-250, job 2 will be 251-500).
PDF creator is an excellent, free piece of software. I rolled it out at my last company for people that needed to create PDF files but did not need to edit them.
Tom