I also wanted to do exactly the same thing and YES, disabling dual graphics in AMDVCC and setting the power option to high performance for the particular program you want to run does work. This causes the discrete GPU to bear all the graphics processing load. I used "GPU temp" to confirm this. I was playing black ops 2 on high performance with dual graphics disabled and checked the GPU load via "GPU temp" and came to the conclusion that only the discrete GPU is being used for graphics processing.
This as a result drastically improved graphics performance as compared to when dual graphics is enabled in the sense that micro stuttering is practically absent.