However, I think the explicit codification also prevents that. AFAIK, once something is in state code as a requirement/prohibited/void action you can't personally waive that.
All the contracts I've seen in California have a disclosure sheet of the law, specifically non-solicitation and IP ownership (on company time/premises with company resources) and don't ask you to waive rights.
My initial expansive statement is based on this personal experience and on discussions with recruitment agents and senior developer friends who have been in the area longer than me, they all told me it is the norm in the industry. Though I admit most of my professional career has been spent on Wall Street and the City in London, so I don't know, maybe I'm misguided?