Ok, flame away, but that idea kicks ass. It's low, and should be pushed back so it hangs out past the rear hatch to be really effective at reducing lift and drag on the car.
I even like the dual element in this application. The only thing it needs to make it complete is some side winglets that hang over the quarters the way the 88 wing does. The 89+ shaped ends just don't work with this setup visual wise.
You could attach the wing to the edges of the hatch. And make the wing sections from CF to be light and strong. The end plates would need to be trimmed, but by moving it back some, your tapping into a known technique used in drag racing, and many other forms to reduce drag, and increase downforce.
That car needs a rear diffuser very bad. The exhaust is interesting. Is that 4" pipe? The wheel houses of this car screem 80's so loud it must really wake up the neighbors and make them want to play some Howard Jones and Wham music till late in the morning.... LOL
Start the flame throwers gentlemen, but I like pushed back low whale tails on the Supra, even ones made of alloy with dual elements. (The ones on tall towers are completely hidious, and the owners should be dipped in honey and placed on ant hills, but this one has potential.)