Good post above, thanks. If you read Leslie McDevitts "Control Unleashed" you will some similarities, with a twist as Premack Principle allows the behaviour.
Another idea is to cue the barking to a command. Once dog learns to bark on command you have control and need a command for not barking too. I haven't tried this but I have used this idea with jumping.
A trick that works for me is laughing at my dog. "Ho, ho, ho, you big silly, that's nothing to bark at. You made a mistake." This works to reassure him that someone coming to our door is not a threat and I'm in charge. After all, would I laugh at a serious threat? Of course this only works for barking when I'm home with him.