Can I adjust my withholding to realize the 7500$ plug in hybrid credit? I want to buy a new car but only if I can get the 7500 back by either lowering tax paid or refund.

I usually receive a refund due to having children, paying for daycare, student loan, wife in college full time, etc. If I can adjust my taxes being withheld to a minimum amount, would I be able to justify the additional cost of the plug in and how?