I know what you mean - it just doesn't seem to go back far enough, but while I suppose a mod is possible, there would be safety concerns. With this car in particular, I'd be loath to go drilling any new holes in the passenger compartment floor.
I'd note that the driver's seat is very adjustable, so don't give up on it too quickly. In addition to the usual fore/aft and seatback angle adjustments, there's also a height adjustment, and you've got lots of headroom to play with. Especially since the steering wheel doesn't tilt/telescope, I had to play around with all these quite a bit to find a good position. At first I thought there was no way I'd manage enough legroom, but finally got everything angled just right, though I can't really vary it.