I used to track my Cayman S before getting my '09 135. The stock handling was horrible, and I was pretty disappointed. I replaced the runflats with Michelin PS2 (225/245), put in the BMW performance suspension, and changed front and rear sub-frame bushings to M3s. Now it's pretty decent handling and the ride on a daily basis is good. Only one day at the track, and it still pushes a bit, but it's much, much better. A square setup would, of course, be better. It's not a Cayman, but it's fun and it wasn't too expensive. In the Porsche, I was in the White run group, so I don't push the car as hard as a hard core driver, but I can make it around the track near the top of my run group.
2009 BMW 135i Coupe, Cashmere Silver, Taupe Leather, BMW Performance Suspension, M3 Front and Rear Subframe Bushings, 225/245 Michelin PS2 Tires