I will never get round to doing this particular mad science project, but you could try creating a aero skirt from a standard one by making an aero-shaped former, dropping a standard skirt on top of it, filling it with water and then gradually bringing the water up to close to boiling point. If it behaves other, ABS-type materials (uniform, thermoplastic, melting point the right side of 100C), you should be able to gently push the standard skirt out into the aero shape. The weight of the water will do some of the job for you, but you'd probably still want to apply some pressure to get nice sharp edges etc. Any weak points could be reinforced, but I suspect there's already enough material to make it work.
Even better, put the whole lot in an oven and vac form it from the outside. Probably less faff, although you might need to jig/insulate the fixed (inboard) points to stop them warping. There will be some paint work to be done with either approach, but that's going to be the case for most people switching skirts anyway.