i know i am Waaaay late on this...but i got it to work by simply going into my control panel and adding a shtml redirect...
so that anytime someone goes to a page that doesnt exist, they get redirected to this new search404 and it seems to do the trick for me....
if you want to use this you will need to adjust the name/location of your search404.php file....
Code:
<HTML>
<head>
<meta HTTP-EQUIV="Refresh" CONTENT="1; URL=search404.php">
</head>
</HTML>
<!--
-->
~TonyD