I'm about 6'3" with a long torso, I fit terribly in small cars. I made the leap into this one because the headroom was just bearable in stock form and at the time it looked like the damotorsports solution was on the horizon. They went radio silent on the product and I started on trying to find my own solution.
Springs stretched and the plastic ties that bind them cut did help, not enough to clear a helmet however.
This is what I ended up doing, and it has been fantastic. Gf needs a booster seat to drive the car comfortably now (she's averageish height 5'7" or so). Shorter people that sit in the car can barely see over the wheel. The seat pan is basically sitting on the floor and thanks to the scooped design of the base just about all the headroom that can be gained is.
http://www.ft86club.com/forums/showthread.php?t=46801
Is your issue slouching for headroom that's causing knees into the wheel?