Simply to update this thread in case it of use to any other users of CodeRunner dabbling in exotic libraries, I had to add an "import os" line:
import os
if 'MPLCONFIGDIR' not in os.environ or os.environ['MPLCONFIGDIR'].startswith('/home'):
import tempfile
os.environ['MPLCONFIGDIR'] = tempfile.mkdtemp()
In our OU theme, it therefore looks like this: