Upload a style sheet called "style.css" to the media folder for any given blog and that style sheet will take precedence over the skin's style sheet.

If you upload style.css to the blogs media directory then it'll automaticaly be included in the skin ;)

inc/model/collections/_blog.class.php :

			/* Add the html for a blog-specified stylesheet
			 * All stylesheets will be included if the blog settings allow it
			 * and the file "style.css" exists. CSS rules say that the latter style sheets can
			 * override earlier stylesheets.
			 */
			case 'blog_css':
				if( $this->allowblogcss
					&& file_exists( $this->get_media_dir(false).'style.css' ) )
				{
					return '<link rel="stylesheet" href="'.$this->get_media_url().'style.css" type="text/css" />';
				}

¥

*edit*
lol *pours drinks* ;)

Awesome, I see now. Thanks!