I'm trying to allow registered site users to add a page to the site but don't want them to see all the C5 menus, sidebars etc. I'd really like them to just click a link and get a pop up window with a few inputs.

When you add a page from the sitemap you get a pop-up composer window (see attached screenshot).
I was wondering if it was possible to add a page like this from the front end of the site somehow?

Many thanks