I find a better way is to use Don Tonberry. You'll need two characters with Auto-Phoenix armours and use either Stoic or Comrade. When you attack DT he'll counter with Karma which deals damage based on the number of fiends killed. The damage will probably kill the character outright, which is where Auto-Phoenix comes in. Only one character will be dead at a time so there's no risk of losing unless you run out of Phoenix Downs.

As Big D said above, use weapons with Triple AP (dropped by One Eye) and customise Overdrive->AP and Triple Overdrive.