Sites that offer the ability to see the desktop site in the footer are actually using two different sites for mobile/desktop.
GP uses responsive design, meaning you’re looking at the same site, it’s just optimized for the screen you’re using.
At this time, I’m not aware of any way to turn off the responsive design on a per-user basis by clicking a link.
I agree that this would be a useful feature, so I’ll look into it to see if it’s even possible.
If you’re wanting that kind of functionality, I suggest giving Jetpack a look – it has a mobile site option: http://jetpack.me/support/mobile-theme/