I have a js script hosted on a URL. My script places a widget View on a site where it is placed. Now for presentation purpose, site owners wants to see the demo with their site structure placed with my widget.

As they are not a technical persons, How do I simplify the process of the demo, so that they can see the demo with their site structure. I understand it is not possible to replicate their UI fully or it will not be time worthy to copy exact. What is best possible way to do this? Also I do not want to spend too much time on creating demos. Is there any free tools available for this purpose?

Thanks.