What is the trick?
The trick is to force computation onto the 3D side. You do this by starting Cudaminer when 2D is running, and then disable 2D. This keeps the 2D running for the program only and forces the 2D computation into the 3D program. Its like running an 8 bit program on a 32 bit system without emulation.
So what are you doing to achieve this?
I was using Asus GPU Tweak to overclock with 2D enabled, starting Cudaminer, then disabling 2D in GPU Tweak. This forced it to use the drivers in 3D.