Great advice. Some bosses do thrive on being in demand by everyone and somehow at the end of the working week, have achieved all they needed to. Organised chaos maybe?
If, however, he feels that he is not getting things done then he needs to be strict with himself and insist that there are certain times when his door is shut and he just gets on with things - definately agree that such times are best done for say an hour or two at a time rather than half a day. Nothing like a deadline creeping up to make my boss hide away - well, he simply shuts the door and diverts phone to me for a couple of hours.
As Atlanta says, be subtle - make him think that you have his interests ar heart (which of course you do

). Am sure at some point in the future when he suddenly realises that his working life is running more smoothly, he will thank you for it.
Good luck - keep us updated on progress!