How can I use intel integrated graphic card for display and use Nvidia discreted card for CUDA only

I just install Cuda 5.5 on Ubuntu 12.04.4.
For needs of long-time GPU computation, I need use CPU with Intel HD4000 acts as display, and use Nvidia GTX660 for computing purpose only.

The trouble I met is that if I set GTX660 as primary graphics, Ubuntu system won’t detect the integrated card (HD4000), which means the command “lspci | grep VGA” return only the info of Nvidia card, no Intel card detected here.

However, if I set Intel HD4000 as the primary graphics in BIOS, the Nvidia module seems to not be running, the most obvious proof is that I cannot run CUDA samples anymore.

is there anyone met such case?