Senator Kerry suggests starting at the source: amend the constitution. From the Huffington Post:
At a hearing on Tuesday, Kerry said that in the short term he wanted Congress to quickly pass countermeasures that would require corporations to get shareholder approval for political spending and prohibit spending by domestic subsidiaries of foreign corporations and government contractors.'But we may also need to think bigger,' Kerry said. 'I think we need a constitutional amendment to make it clear once and for all that corporations do not have the same free speech rights as individuals.'
While, undoubtedly, Justice Scalia would be proud of Senator Kerry for actually changing the constitution's text to effect a change in its meaning, I can't imagine a bigger third-rail for the Senior Senator than running on a platform of "let's fix the first amendment."
More likely than not, Citizens United will be somewhat curtailed by a more mundane act of Congress. Proposals have ranged from requiring shareholder approval of any corporate campaign spending to preventing corporations from listing on exchanges if they fund campaign speech. Whether such an act will withstand the scrutiny of SCOTUS' all seeing eyes is another question (but commentators seem to say no).
So we may be in for a show. Hopefully the 28th Amendment will be a little more spicy than the underwhelming 27th Amendment.