Nightwing

After many many years as Robin and as the leader of the Teen Titans (sort of a Junior Justice League), Dick Grayson decided to leave Gotham City and strike out on his own. He adopts the name Nightwing, and ditches the short pants for what at first was a totally fab disco costume (below, left) but eventually worked it's way into something kinda cool (above).

As Nightwing, Dick becomes the unofficial protector of Bludhaven, a city near Gotham but much smaller (I've heard it compared to Newark, NJ, which is pretty close to New York City). He joins the Bludhaven police force to fight crime and corruption from the inside in addition to his nightime gig as a superhero. But he remains close enough to frequently visit Gotham, taking part in many of the biggest Batman stories of the past two decades, and even briefly taking over as Batman.

Pros: The folks behind the first two movies may not like Robin, but Nightwing would allow them to include Dick Grayson.

Cons: What makes Nightwing interesting in the context of Batman is his previous career as Robin.

How I'd do it: It's a tough one, if you're going to skip Robin entirely, but my best idea would be to have the Grayson family live next door to Wayne Manor. Instead of acrobats, make Dick's mother a gymnast, and Dick is interested in gymnastics as well. Much younger than Bruce, Dick idolizes his older neighbor. When Bruce is off seeing the world and training to fight crime, Dick's parents are killed as well. When Batman starts appearing, Dick understands what would motivate someone to act like that, and how much money it would take to equip Batman. Still idolozing Bruce, Dick decides to join him and makes his own costume (not the disco one), mask, and gear. I think this would do a decent job of replicating the Nightwing/Batman dynamic without the Robin backstory.

Casting Guesses: Milo Ventimiglia (Peter from Heroes) once said he wanted to play Nightwing, and that sounds just fine to me.

Verdict: I guess it's not completely out of the question, but the odds are close enough to zero that I'm just going to call it zero.