Run CSS file through Twig when using {% stylesheets %} tag in Twig with Symfony2
Most common things you'd want to do by processing CSS with Twig should be possible with Sass, LESS or similar, which can be applied as Assetic filters. First tutorial Google threw up was this one: http://alexandre-salome.fr/blog/Sass-Compass-Assetic-In-Ten-Minutes
Admittedly, that doesn't look like much help if you're unable to run Ruby/Node.js/whatever on the production server you're developing for, but it should be possible to create an Assetic filter based on one of the PHP ports of Sass/LESS (assuming they're any good) if that's the case.