Is it possible to specify an ipython_config.py file programmatically?

[Alix Hamilton]

I would like to use a custom ipython_config.py file for notebooks stored in a GitHub repo. I have a test file in the repo that runs the notebooks using the nbconvert ExecutePreprocessor. Right now, the test file temporarily updates the test runner's IPYTHONDIR environment variable during the test run, but I'd prefer to not do this because it seems hacky and I'm worried about editing other contributors' environment variables once others are running the tests. Is there any way to programmatically set the IPython directory or ipython_config.py path without environment variables? And/or is there any way to somehow pass the config to the preprocessor?