It's worse, IIRC all you need to get the tax credit is to purchase the car, with no requirement for KEEPING it. GM also offers a no questions asked 30-day full refund return policy...so -technically- you can buy a volt, return it, and use the original purchase agreement to get your $7500 rebate (which s a TRUE rebate, not a deduction!).
Stupid GM/IRS/government.