Media Uploader in custom path

In,

Dashboard -> Settings -> Media

You can uncheck the,

  ☑ Organize my uploads into month- and year-based folders

…and optionally change the path uploads (but this would effect all uploads of course).

Optionally you can hook onto the upload_dir filter and change the upload path for a given post_type, or for some other given scenario depending upon where and under what condition you are making these uploads.

add_filter( 'upload_dir', 'css_upload_dir' );

function css_upload_dir(){

    global $post;
    $post_id = $post->ID;
    $upload = wp_upload_dir();

    if( "post_type" == get_post_type($post_id) ){

        $custom_dir="/skins/custom-skin/images";
        $upload['path'] = $upload['basedir'] . $custom_dir;
        $upload['url']  = $upload['baseurl'] . $custom_dir;

        return $upload;
    }
}

That should work, though I’ve not tested it, so I’m going off the top my head at the moment.