Weird Software Idea

I'm not a developer, but in light of the 5K iMac and the GPU's present in iMac, I thought of an idea. It's been something that I've wondered for a while. Maybe it wouldn't be useful at all and maybe the 5K iMac's render times compared to the previous generation won't be so bad, but I'm just curious what people think.

Would it be technically possible for someone to invent a program, that allows you to select a certain portion of your machine's display, and turns off the rest, effectively lifting the weight on the GPU to pump the pixels, when you only need a render bar to tick forward until complete? I'm sure the people who would even care about something like that are few (or I'm the only one) but I'm just curious as someone who likes technology, would it be technically possible?

On something like the 5K iMac I wonder what the render time impact would be? What if it was 20%-25%? What if you could just select an area around your render bar counter so you know what progress is being made, hit render, and the rest of your display doesn't tax the GPU? The program could put a little button inside the selection area to turn the rest on when/if you need it to.

Am I nuts lol? Just a goofy idea perhaps...but I wonder what sort of access you'd need within the software of a machine (and the hardware) to do something like that...and even if you could...would it matter?