Bumping this since his birthday is next Tuesday. I'm planning on being at DCA that day, but would be willing to walk over to DL ToonTown if anything is happening.
I haven't really heard of them doing anything special for Mickey's birthday, but I would keep an eye on the Disneyland Today's Facebook/Twitter next Tuesday. You never know if they'll do something and if they do, hopefully they'll announce it!
The last time they did anything it was announced in OC Register that morning. You could still wish Mickey a happy birthday, even if there's nothing official happening.