I have heard just to carry on as normal when your kids do this, the more attention he gets for it, the more the behavior will continue. If he starts yelling in the car about dad, I would just say 'sorry you miss daddy, but you will see him soon. Lets pick out a special treat for daddy while we are at the store and you can give it to him when we get home...' Maybe that would help??
If it makes you feel better, your child doesnt cry for you because he is more secure with you and your attachment. He is not worried because he knows you will come back... Or maybe its because daddy lets him have chocolate milk, pop and unlimited snacks, thats what goes on at my house, lol. Also my husband is a total pushover and lets my dd take her guinea pig in her room. So theres lots of asking for daddy at our house too. Like everything else, this too is a phase, in the meantime you get to enjoy showering without having the door beat down.