I think Ron Moore had it right in his recent commentary - 'Yesterday's Enterprise' should have been the film, with Kirk making the ultimate sacrifice and taking the Enterprise-A back to their deaths to save the future.
The problem is that in the first feature film of the TNG crew, it wouldn't have been the TNG crew at all.
So just say Kirk was the only familiar face on the Enterprise-A, commanding one last training exercise or something. Then you get to focus on him in the Castillo role, interacting with our people.
Obviously to expand to a feature film, you'd have to add a whole new subplot, probably with the evil enemy commander. It needn't be Klingons or an altered timeline of course.