I'm stealing this from someone else, because I can't be bothered to type it all put, but it's how I did it.
"To get technic/tekkit/yogsbox/magic launcher running on the right GPU, open the Nvidia Control Panel. Go to the "Manage 3D settings" section. Pop over to the "Program Settings" tab. Click the "Add" button. Browse to java.exe. The location will vary depending on your OS and java version. On my 64-bit system with Java 7 it is:
C:\Program Files\Java\jre7\bin\java.exe
Where it says, "Select the preferred graphics processor for this program", select "High-performance NVIDIA processor" instead of the default "Use global setting (Auto-select: [...])" option."
If you don't have Integrated Graphics, it won't work, but you'll have the FPS boost already, so don't worry.