How can I install matplotlib for my AWS Elastic Beanstalk application?

I'm having a hell of a time deploying matplotlib on AWS Elastic Beanstalk. I gather that my issue comes from some dependencies and the way that EB deploys packages installed with PIP, and have attempted to follow the instructions here on SO for resolving the issue.

I first tried incrementally deploying, as suggested in the linked answer, by adding pieces of the matplotlib package stack to my requirements.txt file in stages. But this takes forever (for each stage) and is prone to failure and timing out (which seems to leave build directories behind that stall subsequent package installations).

So the simple solution mentioned off-handedly at the end of the answer appeals to me: just eb ssh, activate the virtialenv with

source /opt/python/run/venv/bin/activate

and pip install packages manually. But I can't get this to work either. First I'm often confronted with left-beind build directories (as mentioned above)

pip can't proceed with requirement 'xxxx' due to a pre-existing build directory.
 location: /opt/python/run/venv/build/xxxx
This is likely due to a previous installation that failed.
pip is being responsible and not assuming it can delete this.
Please delete it and try again.

But even after removing these, I consistently get

Exception:
Traceback (most recent call last):
  File "/opt/python/run/venv/lib/python2.7/site-packages/pip/basecommand.py", line 122, in main
    status = self.run(options, args)
  File "/opt/python/run/venv/lib/python2.7/site-packages/pip/commands/install.py", line 278, in run
    requirement_set.prepare_files(finder, force_root_egg_info=self.bundle, bundle=self.bundle)
  File "/opt/python/run/venv/lib/python2.7/site-packages/pip/req.py", line 1197, in prepare_files
    do_download,
  File "/opt/python/run/venv/lib/python2.7/site-packages/pip/req.py", line 1375, in unpack_url
    self.session,
  File "/opt/python/run/venv/lib/python2.7/site-packages/pip/download.py", line 582, in unpack_http_url
    unpack_file(temp_location, location, content_type, link)
  File "/opt/python/run/venv/lib/python2.7/site-packages/pip/util.py", line 625, in unpack_file
    untar_file(filename, location)
  File "/opt/python/run/venv/lib/python2.7/site-packages/pip/util.py", line 533, in untar_file
    os.makedirs(location)
  File "/opt/python/run/venv/lib64/python2.7/os.py", line 157, in makedirs
    mkdir(name, mode)
OSError: [Errno 13] Permission denied: '/opt/python/run/venv/build/xxxx'

in response to pip install xxxx (and sudo pip fails with sudo: pip: command not found).

What can I do to get this working on AWS-EB? On Heroku, I can deploy and run the same application without a hitch with a single click.

---

FWIW, I have a .ebextensions/software.config with

packages:
  yum:
    gcc-c++: []
    gcc-gfortran: []
    python-devel: []
    atlas-sse3-devel: []
    lapack-devel: []
    libpng-devel: []
    freetype-devel: []
    zlib-devel: []

and a requirements.txt that ends with

pytz==2014.10
pyparsing==2.0.3
python-dateutil==2.4.0
nose==1.3.4
six>=1.8.0
mock==1.0.1

numpy==1.9.1

matplotlib==1.4.2

After about 4 hours, I've gotten far as numpy (as reported by pip list in the EB virtualenv).