I couldn't get a nice square fit on the bolt from my impact gun, but that will work nicely if you've got a gun that fits squarely on the bolt. I sprayed some penetrating lube onto the bolt and let it sit an hour. I placed the end of my breaker bar under the passenger side frame rail (socket squarely on the bolt of course) and had my wife momentarily turn the car over with the key. That quickly did the trick!
Before doing this, I removed the dist cap to minimize the chance of the car starting, but to be even more safe, you may want to remove the spark plugs to eliminate any chance of compression ignition.