ComponentJS has a very powerful builder which you can tie into to handle various use-cases you may have. A common one is using a CSS preprocessor. I'm a big fan of stylus so I'm going to go over how I wrote component-stylus to transpile stylus in-place.
NOTE: I would NOT recommend using this in its current form for work you plan on sharing with the componentJS community. Components should be pure js / css / html.
When first starting out people will most likely begin using the vanilla 'component build' command to package up their components. While this allows for people to get their feet wet quickly, they are missing out on our friend component-builder.