This might be not the nicest way but when I really want something and I know we might disagree on weather or not it is necessary I bring it up to him like it is fact or going to happen I am really nice and carefull about the words I use.
For instance, I would tell him I have to run to the store and pick up a few harnesses because I know the ones I have will not work for the new puppy. Or hey babe I am going to make dinner early on tues. because I am meeting so and so to pick up my new baby but I will have it on low for when you get home
Or I got you these really great seats at the game call up a friend because I would like the house quiet when the puppy comes home this weekend. Usually he cant help but smile when I do this, then he gives me this look like do I have a choice. It worked for when I got Copper, new funiture, extra clothes and accessories for Copper or me, a trip to Vegas
hehe