if that doesn't help, you can always run a less agressive pad in the rear to compensate. I've found 'street' pads like hps work fine in the rear for track days - even if you have a very agressive pad up front, depending on what your bias is (obviously it's changed a lot due to the swept area increase up front).

Something else you might want to look into is a bias controller. I know they can be a pain, but to fine tune I can't think of a better way to do it.