You can also use the following in an .htaccess file to redirect instead of giving a 404.
# 404 Redirects
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^/?(.*)$ /index.php?url=$1 [L]
Replace /index.php?url=$1 with whatever URL you want to redirect it to.
Hope this helps.