As an Ubuntu user of one of these laptops (nVidia Optimus: Intel + nVidia), I can tell you right now that the whole switchable graphics thing is a nightmare. It's getting better, slowly, but you run across all sorts of problems. I suggest looking into the Bumblebee Project (apparently I'm too new to post links, but Google "bumblebee nvidia" and you should be able to find something), at least for the nVidia side of things.
Basically, though, my understanding of Optimus is that, even though it has a dedicated GPU, everything still gets sent through the Intel GPU before being displayed. Therefore, you cannot turn off the Intel GPU, but you can still leverage the nVidia card. Nonetheless, it seems what you're trying to accomplish can already be done through the use of Bumblebee's optirun command. The basic state of things is that everything goes through the Intel GPU, but when you precede a command with "optirun" it will turn on your dedicated card and use it instead.
Frankly, though, it's all just a big pain. While using Ubuntu I very, very rarely touch my nVidia card. The Intel GPU built into the Core i3's seems to be plenty to handle any tasks I've thrown at it. Basic day to day use sort of things.