how to disable support for mining on the CPU?
to disable individual devices you should read this thread; it already explains how to modify the settings and comment out the necessary lines and disable/change different devices in the nvidia.txt, cpu.txt and amd.txt....
What would be better is you should check readme.md, compile.md, etc on the official github:
https://github.com/fireice-uk/xmr-stak Just scroll down; there's links there to each subject. It goes into great detail.
I didn't write the program, I just compiled the source with no devfee.