I use the same method as CanAutM3 as well as use a CGLock and a volleyball knee pad on my left knee to help brace myself against the door.
At Sebring, a similarly prepped GT3RS 4.0 is about 9 seconds faster around a 2:30ish road course.
I'm 6'0 and have a sedan with sunroof and no issues with clearance. You may have a long torso...but so do I. Maybe just add a little recline and get your seat bottom forward. You can use your telescoping steering wheel to get your arm distance right.