Have you tried using bumblebee[1]? I use it on my Samsung QX411 which has an NVidia GeForce GT 525M video card along with the onboard Intel. The Intel card is used by default at all times. If you want to run a program using the NVidia card, just prepend 'optirun' to the command.
[1] https://wiki.ubuntu.com/Bumblebee