Your suggestions work well and I've been using them for a while. Another option
is to have httrack pretend to be a web spider like Googlebot. Some sites let
the bots in while unregistered users don't get in. I should point out that
some sites don't behave the same while pretending to be a spider so I wouldn't
suggest you use it all of the time.

I have found one site that is proving rather interesting to copy. It's an
adult site that displays fine if you use a browser and click on one of the
thumbnails, but if you try to go directly to one of the images you will get a
Forbidden message. It's at www.creampie-4you.co.uk/avidols/akira/akira05.html
I haven't given up on it since I consider this a challenge but it is proving
rather challenging. Presumably there's some code running on the server that
detects how you are entering the site.