put the thumb in the ball is a very ignorant statement. there are countless things you can do to help keep the ball on the right side of the head pin. the first and foremost of course is to learn proper technique. you cant go to the lanes and throw it 10mph and rip on it as hard as you can and actually expect results. try and help them learn to adjust, and keep there ball in heavier volumes of oil longer. a cheaper, less reactive ball is also a good option. if they refuse to buy one, tell them to get an older, perhaps urethane, ball off the rack and use that. there should not be a problem as long as there fingers can fit in the ball, they should be fine. no thumb = can throw almost anyones ball as long as the holes aren't way too small. try and explain to them that they need to develop ball speed, and learn to control the amount of tilt and revrate. 99% of the time, you should be using less than 75-80% of what you can actually put on the ball with no thumb, thats what ive found anyways. power and speed control is the name of the game. 4000 grit and polish might help get the ball down the lane, but it will only make the reaction off the dry stronger. i would suggest 4000 grit finish to help get the ball down the lane, but also make a less drastic flip off the dry. telling them to just completely change is a very dumb thing to do, and it will only make them not listen to you. if someone is willing to accept your help, dont slap them in the face with a big, "your bowling wrong, change completely or quit."