And now a miracle happens...

Sorry, I don't know any easy way. First you have to create a skin (if you want the same look and feel). Second you have to copy the content. Which can be quite some work if you want to use the most appropriate dnn modules.
Short cuts are possible. E.g. you could use the html/text module for every piece of content (just copy and past the html). But you miss out on the nice dnn stuff, e.g. expiration in announcements.
Another possibility: if you have an elaborate form, you can use an iframe to the original page, and keep using this form outside of dnn.

Good luck

Peter