That is precisely what the court ordered. To wit, "If the First Amendment has any force, it prohibits Congress from fining or jailing citizens, or associations of citizens, for simply engaging in political speech. If the antidistortion rationale were to be accepted, however, it would permit Government to ban political speech simply because the speaker is an association that has taken on the corporate form. "

It's fairly clear throughout the ruling[1] that the Justices are not relying on corporate personhood, but the freedom of association argument. It is a media myth that the case was about 'corporations are people, too!'

[1] http://www.supremecourt.gov/opinions/09pdf/08-205.pdf