If you live in CA you must own/drive the vehicle for a certain amount of time to get the rebate. (It used to be 30 months.) If you sell/return the car before that time, you have to tell CARB and give the rebate back. Now, if you didn't know that you could get the CA rebate for a lease, so you didn't apply, then no worries. Also, they changed the law last year so that the amount of rebate MAY depend on your income (poor people get more money). Also, if you make a LOT of money, you have to choose between the rebate and the HOV sticker. (If they haven't changed the law yet again.)
I believe that there is no requirement to keep the vehicle for any specific amount of time for the fed tax credit (which you wouldn't have gotten anyways, since you are leasing). If you didn't pay a huge amount up front (you'll never get the up-front payment back from GM), then maybe you can manage to find somebody who might like to take over the lease. Or, maybe you can find somebody who will give you a prorated 33% of your "drive off" fee. You will have to pay a "lease transfer fee", but you would avoid paying the "lease return fee" (which is called something else, but there is a fee).
And the fed tax credit is a CREDIT, not a rebate. If your total tax bill is (say) $6000, then that's all that you get back - the credit only offsets taxes and it can't be carried forward. Note, I'm not saying that your *balance still to pay* has to be $7500. If you are responsible for $8000 for the entire year, and have already paid $7000, normally owing $1000 - you would instead get a refund from the IRS (your bill was $8K, you have a tax credit of $7.5K, total tax becomes $500, you already paid $7000, so you would get a refund check for $6500).
If you don't make enough money to have a total tax bill of at least $7500 :
- sell some stock (if you can do that)
- open a Roth IRA, and move money out of your traditional IRA into the Roth (go talk to an accountant about this option)
- talk your boss into giving you a bonus
In either case, "make" enough so your total tax bill would be (say) $7600, so you can take the full tax credit.