That one is tough. I've been working on something like this but haven't yet sent it out into the world to see how it is received. I wrote a little script in PHP using the CURL module that does the mirroring. Part of the trick is that I have a sitemap in XML that is generated by a server side script. I had to use PHP because of the site's authentication but you might do better with an HTML Application.
“The power of the Web is in its universality. Access by everyone regardless of disability is an essential aspect.”
—Tim Berners-Lee, W3C Director and inventor of the World Wide Web