Can he see you out the back window? What I found that seems to work for anyone I've directed back is this:
-Stand by the ball.
-Hold one hand up edgewise with your pinky toward the truck (think half of prayer hands).
-As the truck backs, tilt your fingers left or right as needed to direct.
-When within a couple feet of the ball, hold your thumb and index finger wide apart, then slowly and proportionally squeeze them smaller as the ball approaches. Your finger should touch your thumb right as the ball is under the coupler.
With this method you don't have to run in and out to give directions.
