so, i'm working on a 'thing'. i have a friend who is good with fiberglass who is bonding a set of speedster humps to a tonneau cover (the metal lid that covers the roof). when done he is going to take a mold and be able to make a lightweight one-piece panel that replaces the metal tonneau cover and covers the rear area behind the seat to provide better aero. it will mount at the spinlock locations (and perhaps a latch just in front of the third brake light if i get around to it).
you won't be able to use the standard convertible top with it. if you want light, remove the top - 6 bolts gets you 50 pounds - run with the speedster setup at the track (factory aero so no point issues) reinstall roof and cover for taking GF to dinner.
thinking i will fabricate a speedster style top to go with it - use the front part of the old convertible top to mount to the windshield, drape over the roll bar (sew in a spreader bar that velcros to the roll bar) then extend back with some custom canvas. it can store under the speeder panel when not in use. ** edit: like in the image a bit.
*** if you want to get really crazy, trim down the windshield for a real speedster look (Lexan?) and get one of these:
Boxster Tonneau - Pelican Parts Technical BBS
no going back from something like that, however.