If you are adding pages to a WordPress site outside of WordPress then I don't think you can easily achieve what you are looking to do. WordPress builds pages dynamically and in doing so builds each URl. My guess would that adding a page manually means that WordPress won't even know it is there.
I might be wrong but to get wordpress to include your manually added pages in its permalink structure, you will need more than a plugin!
I wonder if you could do it with an iframe?
You can get plugins for that but I guess it would be fairly straightforward to achieve in the text editor. I've never used an iframe intentionally. You could modify your manually added page to remove the content you don't need and then call it into the page with an iframe?