Again, others have said it - convince him to either do it right (drill the roof) or don't install the radios. You either get subpar performance, which means you might as well not bother, or you do it right and use the radios to their full potential. Show him this thread if you have to (minus the silly "window mount" comment...those are pathetic antennas, I don't care what anyone says...).
He'll ugly up his truck with a lousy install but won't properly drill and mount the antennas? It's a much cleaner look to do it right and drill...plus, as we all know, the performance is best then.