trait HtmlHelpers {
  protected def css(src:String) = <link href={src} media="screen" rel="stylesheet" type="text/css" />
}

trait BlueprintHelpers {
  // this line does the magic
  this: HtmlHelpers =>

  def screen:Elem = css("blueprint/screen.css")
  def ie:Node = 
    <!--[if lt IE 8]><link rel="stylesheet" href="/css/blueprint/ie.css" 
      type="text/css" media="screen, projection" /><![endif]-->
}