you can adjust the brake pedal down a bit and try to adjust the accel pedal up a bit.
if that still doesn't get you close, you could extend the accel-pedal rod or put a block of wood on top of the accel pedal.
i actually have the same problem, but i don't need to heel-toe
i just shift faster and blip the throttle when i'm done braking before i release the clutch. hard to describe, but it works well if you're fast enough ...
brake really hard, while still on the brake (towards the very end of braking) step on the clutch, then get off the brake, blip throttle while releasing the clutch and step on the gas.
all that within a 10th of a second. werks for me ...
Andy
PS: sometimes you actually WANT the rear to unsettle and don't blip on purpose. it can help you to get your ass around those tight corners after a long straight ...