This is an innovative idea, Frame. I have a nagging memory that tells me Superman's vision abilities won't work on lead at all, and that's why Clark's lenses were made of leaded glass, so he wouldn't accidentally ignite something or inadvertantly become a peeping SuperTom. I think that was also why Clark had to lower his glasses to use his X-ray, heat, or telescopic vision.
But melting the Kryptonite was brilliant! I don't know why no one else ever used that trick. And since this was obviously some kind of industrial use building, the Kryptonite just flowed down the floor drain into the sewer system, where it would spread itself too thin to be recovered and be too dissipated to injure Superman.
I just wish I'd thought of it first.
