I am developing a sphinx based collaborative writing tool. Users access the web application (developed in python/Flask) to write a book in sphinx and compile it to pdf.
Assuming you used sphinx-quickstart to generate your initial Sphinx documentation set with a makefile, then you can use make to build docs, which in turn uses the Sphinx tool sphinx-build. You can pass the -w stderr.
Note that options passed through the command line override any other options set in the makefile and conf.py.