Not having Shatner was one the best decisions made in making XI. Kirk's dead and should stay dead.
Eh, I don't think old-spock looking at a hologram of his old friend, or visualizing shatner during the mind meld, or something like that, would have necessarily hurt or helped the movie. They already shoe-horned Nimoy in so it's not like it would have been any less credible.
However, I still think the best use of Shatner in the new movies would be to make him some kind of comic-relief bartender, in a cameo or something.
Just imagine how hilarious it would be to have a quick scene of Shatner as a bolian bartender or something. Serving drinks and inadvertently giving some valuable piece of advice to Nu-kirk. Seeing shat in alien makeup for the first time after all these years would be pretty funny... and something tells me he'd make an excellent bartender.