Having your ad-libs stand out from your main rap vocal is a necessary step to making your song sound unique and different.  I use a few different techniques to achieve this. One is filtering the ad libs, so you have no low end. Another is to add more reverb than would ever be on the main vocal. The 3rd way is to use auto-pan to move the adlibs from speaker to speaker.

Check out the video below to see these techniques in action!