After Citizens United: Bringing the Hatch Act up to date

In the wake of the Supreme Court's decision in the Citizens United case to invalidate certain restrictions on corporate spending in election and issue campaigns, Bruce Ackerman and Ian Ayres suggest in the Washington Post today that Congress can nonetheless take steps to keep politics in the hands of literal people, rather than figurative ones:

...Many suppose that the court has made it impossible for Congress to restrict corporate speech. But this is wrong. While Congress can't issue a broad ban on all companies, it can target the very large class that does business with the federal government and ban those companies from "endorsing or opposing a candidate for public office."