Is nigh on impossible to do - but a Nismo 380RS pedal helps - there's even one for sale here http://www.350z-uk.com/forum/viewtopic.php?f=32&t=44421
might get one when ive got some more cash, the only time i can heel and toes succesfully is under very harsh braking.
other than that as said the brake pedal is way to high above the accelerator, my old civic type r was perfect for heel and toeing.