The Swedish Method
This is, of course, only safe and practical on the engine that is still in a car, but it is recommended by Volvo factory trainers and also frequently used by SAAB techs, who have to change a lot of harmonic balancers on old generation 900 models because they are located at the firewall end, right over the headers, which cook out the rubber, especially on turbo models.
You take your breaker bar along with the cheater pipe and put the socket on the nut, then brace, prop, and bungee all that very carefully in place so that it can't move, with the cheater tightly wedged against the bottom of the car's right frame rail so that it can't possibly turn in the direction of normal engine rotation. When all is secure, you disable the spark, then get in the car and hit the starter a few times. If that doesn't break the bolt loose, you need to consult a pro with a bigger air wrench and 3/4 drive sockets.