title: Can I show a fallback ad if my adsense for search unit is empty?
body: <p>We've just added <a href="https://code.google.com/apis/custom-search-ads/" rel="nofollow">adsense for search</a> to our site.  We have three units on the page, and sometimes there aren't enough ads to fill all three, so they end up empty.  When this happens, we'd like to show some alternative content.  Is this possible, and if so, how?</p>