Re-direct when a subdomain is mis-spelled?

Hi

I'm using the multisite plugin with Wordpress Multisite.

As you can see, it works great with my TLD and my subdomains.

However, if a subdomain is mis-splled by a user, it brings up an error page showing the site that is my main WP site.

See here for an example:
http://screencast.com/t/zwyTLDUA5

Is there a way for me to stop this and have the error page be generic?

thanks for your help, Andrew