title: Drawing only boundaries of stat_smooth in ggplot2
body: <p>When using <a href="http://docs.ggplot2.org/0.9.3.1/stat_smooth.html"><code>stat_smooth()</code></a> with <code>geom_point</code> is there a way to remove the shaded fit region, but only draw its outer bounds? I know I can remove the shaded region with something like:</p>
  
  <pre><code> geom_point(aes(x=x, y=y)) + geom_stat(aes(x=x, y=y), alpha=0)
  </code></pre>
  
  <p>but how can I make the outer bounds of it (outer curves) still visible as faint black lines?</p>