I've got a strange idea. Where I work, we cut parts out of rolls of .095" spring steel with a laser. There's 3-4 feet left over at the end of the roll, that we just toss. The pieces are 5 1/2 inches wide.
I could bolt legs to it, spring perches on the ends of the legs, and have a flat sway bar. A stiffener could be added to one edge to keep it from bowing in the middle. There is plenty of room under the car near the rear axle for this to fit.
I'll have to see what I can make this weekend.