I've done that and it worked out so well he kept that dog in the divorce. When my ex and I were living in NYC, we'd agreed no new dog until we left the city. I went into a Petco to pick up some food for the other dog and (as always) held a rescue puppy. (I always figure other potential adopters are more likely to stop if somebody's already there.)
I fell in love with the pup and adopted her. The ex was a bit frustrated at first, but he loved her, too. She was a bit of a nightmare and had some behaviour problems, but she was a great dog. A few years later, when we divorced and I moved over here, he kept Lola. She had very much become his dog.
Similarly, before Poppy came over to the UK, I pointed out a different Pomeranian to Adam. He thought they were horrible little fluffy yappy dogs and was a little disappointed that Poppy was one of 'those things.' Then he met her and loved her. (He's not always happy with her, but he does love her.)