I'll then ask how patrons can tip them and them alone.
In other words, "How can I make it possible for you to stiff the people you would otherwise share tips with, people who will make your job miserable if they catch wind of what you are doing? How can I ensure you will be the least liked waiter in the restaurant?"
Next, how do you plan on enforcing that once you leave the establishment? Ask for an accounting of the server's tip income and what they shared with other workers?