Dynamic CSS: getting data into the file (again)

[eluser]codex[/eluser]
You can put php in a css file by adding header('text/css'), and that all works fine. But I'd like to add <?php base_url()?> (and get data from a db) to the file, but this isn't available in a regular php file. How do you extend the file so that the ci instance is available?

I already asked this question some time ago, but haven't been able to find a solution yet. Here's the original post: http://ellislab.com/forums/viewthread/77954/