Based on johannr's suggestion, after a little fiddling, I did get notebook to run. Based on this stack overflow question, I first installed pip, then uninstalled ipython, and reinstalled with the [all] option to include all dependencies.
Install pip:
$ easy_install --install-dir='/Applications/FEniCS.app/Contents/Resources/lib/python2.7/site-packages' pip
$ ln -s /Applications/FEniCS.app/Contents/Resources/lib/python2.7/site-packages/pip /Applications/FEniCS.app/Contents/Resources/bin/pip
Uninstall and reinstall ipython:
pip uninstall ipython
pip install --target='/Applications/FEniCS.app/Contents/Resources/lib/python2.7/site-packages' ipython[all]