No, it's not possible. Nor will it ever become possible, on any operating system.
What Apple and some other dual-graphics laptops provide is called Hybrid Power, for energy efficiency. You can only use one of the video processors at once. This is the only possibility for a laptop with a 9600M GT paired with a 9400M integrated (MBP).
To use both cards at the same time is called GeForce Boost, and it is only available to lower end models (eg. a GeForce 9500M G paired with a 9100M G integrated on the motherboard).
The reason you can't have GeForce Boost with higher end graphics cards is that you won't get any performance gains when pairing a low end card with a much better one (like the 9600M GT), because the slower one will just drag the performance down (you'll know why if you know how SLI works).