I have a kickass strategy that wins 99% of the time for the special battles, but it involves Omnislash and Mime and doesn't net you much in the way of BP. If you want that, I'll post it; for now, good luck, wear a ribbon, keep a variety of Enemy Skills and Summons and Magic on hand (also Deathblow and Counter). Make sure you have plenty of remedies and items that inflict damage (Grenades suck, get Right Arms or 8mm Cannons). If you happen to have anything like Cover or Cure paired with All, get rid of it. (Time + All is OK since it lets you use Slow/Stop All.)

Wear a Ribbon, heal as needed, and keep fighting. Make sure you have at least 100+GP beforehand, because it would really suck to almost have enough BP and then run out of GP.