Hi!
This hopefully should be an interesting job :)
If your site is responsive using media queries, we can create two stylesheets, one with the media queries and one without. Using a button, we can choose which stylesheet is loaded and can switch between them. Accordingly, the site will shift between responsive and full size.
The reason I am bidding on this is because if you'll check my reviews, you'll see that I am particularly good with coming up with solutions that others can't, especially when it comes to wordpress.
Hoping to hear from you!
Have a good day!