This isn't the how do I defraud the state and get away with it. What you perceive as undetectable to the state is not an issue here. You must report any self employment you do as YOU WORK IT. Your reports to the EDD specifically ask so this should NOT be a surprise to you.

You lie, they find out (they do follow up on things from time to time), you'll not only be asked to repay the overpayment but you may be subject to penalty and criminal prosecution.