First off, roll the ball and mark the flare rings/track flare around the ball. It depends if you want to also take out top weight or add side weight.

You can put a hole right above the bridge. This will take out equal top and finger weight. This may not be bad, but you have to see if the ball will flare over the hole. If it does, you'll have to move the hole to the right, which in turn will take out side weight. This will give your ball less reaction on the back end.

You can possibly take out finger, top and add side weight, which will give you a stronger backend. Find where the bowtie of your track flare is. From there, you can drill a hole to the left of it. Again, place it so it doesn't hit the holes. This will add side weight as well as take out finger and top, giving you a stronger backend. =:^D