I agree that having a cloth insert on the seat options for the Cayman would be great. To do this one option may be to order "leather to match" for the center of the seat, and supply a sample of your favorite cloth color and pattern. This will probably take a long time, be very expensive, and take multiple times to get the order to stick.
Another way to get cloth which is probably an easier and cheaper way, is to order the seat in the color leather you want, and then have an upholstery shop take out the center sections (they pop out as they are held in with nylon fasteners) and recover the centers with the cloth and pattern you want. Any reputable auto upholstery shop will have catalogs with seat fabric that matches most older cars.
This is what I plan to do. My thinking right now is to order a Cayman with the Coco (or Terracotta) leather, and replace the center seat sections with a brown or reddish brown plaid or hounds-tooth on beige or white background.
I am also looking at Forest Green as the exterior color. Not contemporary Porsche Colors, but rather heritage Porsche colors.