Train cats to use a toilet and flush it

I've see those inserts they sell for your toilet to use to teach your cat. I tried it once with one cat I had that was facinated with watching the toilet flush. I tried the home made version of a disposable aluminum roasting pan. He did all right until it got to the part of taking the pan out entirely. He couldn't get the concept of standing on the seat and not down in the pan to go.