Under what conditions are "suicide knobs" legal in California?

I'm looking to get my driver's license soon in the state of California, but I suffer from a mild form of cerebral palsy that affects my left arm and leg. My dad recommends that I look into the legality of steering wheel knobs, as using one might improve my driving. I haven't been able to find specific laws on the subject, so can anyone clarify some specifics? Thank you ahead of time.