I know I've read that you shouldn't mix tires...at least not 1 vs. 3. I think you could easily get away with 2 of the same, as long as the matching pairs are either on the front or back. (I could be totally wrong though...let's see what the experts suggest!)
This doesn't help you, but within a few weeks of buying my Volt I went to Discount Tire and bought the tire warranty certs from them. They were happy to sell them to me. Covers lifetime balance & rotation, as well as flat repair. Also will cover accidental damage/road hazards similar to what you experienced.
2012 Cyber Gray, Navi, Rear Cam, Bose, Premium Trim, Polished Chrome Wheels