If you download the specific site using normal settings ( external links, embed
external images ... ) then you will see the content warning screen if you open
your mirrored page.

the trick is: open the sites, where you want to remove the warning with your
favourite editor ( mine is vim :) ) then search for visibility:visible and
visibility:invisible.

the first one is the content warning ( an injected iframe, should begin with
<iframe ... ) and the second is the page you would like to see.

now the only thing you have to do is to change the first one to invisible (
the warning ) and the second to visible ( the body ).