[The Radium King]

the spyder has an 11.4 hp/weight ration (hp*100/weight) where as the 986S has 8.9. even losing 200 lb and gaining 35 hp (the max you probably could expect with bolt-ons and a streetable weight loss program) you would still only hit 10.9.

a 987S, however, could easily be converted. from wiki:

... the Boxster Spyder will be the lightest Porsche on the market, weighing 2,811 pounds, a full 176 pounds lighter than a Boxster S. This has been achieved through the elimination of the conventional soft top's operating mechanism, the radio/PCM unit, air conditioning, storage compartments, handles, cupholders and large LED light modules on the front fascia. The vehicle will ride on a firmer suspension than the other Boxster models, and will also be almost one inch lower in order to have firmer handling. A manually operated canvas top, sports bucket seats and two signature humps running along the back of the vehicle provide characteristic design elements. It will offer a six-cylinder boxer engine with 320 horsepower and 273 lb·ft of torque, a 10 hp increase over the engine in the Boxster S and the same engine used in the related Cayman S.

so, a/c delete, gt3 seats, remove roof motors, PSS9 suspension, lightweight battery, lightweight wheels, RS door pulls, intake, exhaust, tune, etc., will get you there. $10k in upgrades; more if you want it to look like the spyder (and not just perform like it).