Also, there is the claims that:
He is actually the rear dome at the end of the Enterprise saucer (unlikely they'd make him so prominent and he'd be like 10 times too big).
He's on a forklift that passes behind Kirk and McCoy before they depart for the Enterprise (it obviously looked like just a weird reflection to me).
He is in the transporter room when Spock and Sarek talk behind some glass on one side (I didn't see anything and it looks like the same lights all over).
Someone claimed he was on hull of the Enterprise in the last shot of the movie (I didn't see it in the place describe).
And the only credible sounding one which I haven't had the chance to check out was when the camera first pans along the Kelvin at the start of the movie, a set of windows goes by and you briefly see R2 in the window before the camera continues to pan.
I was the one who made the debris barrel roll spotting, but its obviously difficult to point out the exact debris at the exact moment without a good version of the movie available and a screenshot.