I saw a picture where someone had done up their 986 to be a permanent Spyder-style car. It had a canvas cover behind the roll hoops where the folded top and clamshell would normally sit, but as far as I know there is no sort of top for the car and it is strictly a nice weather car.
It's actually the yellow car on the cover of Wayne's 101 Projects book, and you can kind of make out in that picture how the rear of the car just flattens out behind the hoops. I'll have to see if I can find one of Wayne's pictures from it.
Ah, here we go:
I have no idea what work was involved to make it that way...it looks like the clamshell piece is still there under the material to keep the shape, though. Maybe Wayne might know more or be able to get you in contact with the person who had the work done to their car.