Transformers Live Action Movie Blog has noticed on an unofficial Transformers Facebook page a possible hint that the blue Mercedes is indeed Wheeljack. The picture on the left shows a shadow of Wheeljack in the Rising Storm comic and on the right is a screenshot of possibly Wheeljack in the theatrical trailer. A similarity between the two I've noticed is the left shoulder (from your view). In the Rising Storm comics Wheeljack is badly injured and Ratchet says he can fix him but he won't be the same, so how he looks will not be the same from the comic to the movie.
UPDATE: My mistake- The comic picture is from the DOTM comic adaptation, not Rising Storm.