I haven't before, but I'm going to in Black 2. I'm going to trade the Tepig I select to Black for my shiny Charmander as soon as I can. I just did a game with the Unova starters, and I want to mix it up a little.
(The Tepig will be going to a good home, though- I plan to use him in Black. Plus, I need Emboar to complete the Unova dex, so, hey, two birds with one stone.)