Kink in the Hose

How in the world do you get a boy to stop putting the Vulcan-neck-pinch-death-grip on his member and spraying everything in front of him when he's going to the bathroom?

Well, for sure, saying "Don'tPinchDon'tPinchDon'tPinch stop pinching it let go!" only draws undue attention to yourself and the fact that the wall is now a sticky mess.

"But daddy, I have to hold it so pee doesn't go everywere."