Rails - Dec 2004 - Redirecting errors to 404.html & 505.html for non localhost IP''s

Hi,
I remember a very long time ago reading that somewhere I could set my rails app
to serve up the default rails error pages when viewed from localhost or a
specified IP. 
And then redirect to 404.html or 505.html for all other IP addresses.

I''ve been digging around and I just can''t seem to find this
bit of info again.
Anyone know what I''m talking about?

Thanks in advance

Jonathan