Tip MOSTLY in cash. Then put a tiny tip amount on the credit card {say 2%}.
If the IRS audits that restaurant, it will have to believe that 2% is what you tip. If you tip All in cash, the IRS can estimate your tip rate & tax the wait person on that estimated income.
Hmm, good tip. I will have to remember to do that. I used to work as a delivery driver and I used to add about 10 percent to my income as tip income.