I machined a aluminum angle and mounted to the existing screw holes that are for the license plate lamp then attached 2 small 3 1/2 Dia. 55W halogen lights I bought from J. C. Whitney. (P/N 12YB3319X $17.95)
I can still access the soft top easily to remove & unzip the rear window.  They work great for backing up, I can finally see what back there.  Having 2 lights there I get a wider spread of light.