How about "Your Dudeness" or "El Duderino", if you're not into the whole brevity thing? Petty namecalling is stupid, but "dude" is a sign of (modest) respect.
Seriously, as a foreigner I reckon that the office of the President of the United States needs to be taken down a few notches. I mean, I accept that the dude needs a private jet, but does it really have to be a 747 and called Air Force One? I accept that the dude needs a limo instead of driving himself around, but does it really need to be a custom-built limo? I accept that the guy can have a nice executive mansion, but does he really need his own seal, his own theme tune and a standing ovation every time he shows up to talk to Congress?
There's a difference between the need for more civil discourse and the need to address people by their titles. Uncivil discourse is unproductive, but I don't think "dude" is particularly uncivil. "King George" is.
It's a pet peeve of mine when people call President Bush 'King George' or other epithets, even if I do disagree with his policies.