This is only tested against Python 2.7. Python 3.3 contains many changes, so it may or may not work--you're on your own for that.
You only need epubsplit.py and BeautifulSoup.py from the
epubsplit source repository. (I mistyped when I wrote epubmerger.py--sorry.) Put them in the directory you plan to run them from. (I don't know how you'd go about adding a python script to your path or anything like that.)
Run 'python epubsplit.py' to get the CLI options.
Run 'python epubsplit.py input.epub' to get a list of split point 'lines' in the source epub. Each 'line' is equivalent to the lines presented in the plugin GUI.
To do the actual split, run 'python epubsplit.py -o output.epub input.epub 0 1 2' for example, to split off the first 3 lines.