I remember looking to do the same thing a few years ago and lo and behold, I still had the link in deep archive: http://forums.macrumors.com/showthread.php?t=1354754
A MacRumors Forums member named Oligarch put together a bunch of command-line pdf tools, which can be downloaded from this link: http://users.skynet.be/tools/
The pdfburst command is what you need:
pdfburst -- burst (split) PDF documents into single pages
pdfburst file [path]
The pdfburst utility bursts (splits) the PDF document file into single
pages which it writes to path, appended by an underscore character and
zero-padded page numbers.
If file is a single dash (-), the PDF document is read from the standard
If path is omitted, the base name (last path component) of file is used
and the single page files are created in the current working directory.
If path ends with a slash (/), it designates a directory and the single
page files are named with just the page number.
Missing directories along path are created.