Theme Viewer Question

I know all about the Theme Switcher plugin where I can let users select what theme they want to use to browse my site.
I have themes for download that I want them to be able to preview. I don’t want them to browse my website with the themes but a mockup web blog. How would I go about going that? Should I create another blog to do this? Or does anyone know of a plugin that would do what I want (which I prefer because it is easier).