Randy Barnett, a law professor who a commenter notes should be added to our list of ObamaCare Constitutional skeptics, has offered a draft of a Constitutional amendment he calls the "Federalism Restoration Amendment":
Section 1. The legislative power of Congress shall not be construed to include mandating, regulating, or prohibiting the private health insurance of any person not an employee of the federal government.
Section 2. Whenever two thirds of the Governors of the several States concur, they may rescind any law or regulation of the United States, or they may propose amendments to this Constitution, which shall be valid to all intents and purposes, as part of this Constitution, when ratified by the Legislatures of three fourths of the several States.
The Volokh Conspiracy blog, where the draft was posted, has a lengthy comments thread with feedback.