I personally would not ever do it, but that's me. Some cats choose to do it, obviously they are comfortable with it, but I would not want to have my cat use the toilet if he was not comfortable with it.
If you do try this remember that is natural for cats to only want to go in absorbent places like fabric and sand so they may choose carpet over toilet, I would have another litter box available until it's obvious the cat is fine using the toilet without any sort of litter box in it.
Here is something that shows how to do it:
How to Toilet-Train Your Cat
I know if I tried to touch my cat while he was about to go potty (to adjust his feet) he would be out of that bathroom without thinking twice and would surely be hesitant to try again. Same thing if he peed/pooped and water splashed up on him.
I don't know why having a cat use the toilet bothers me so much, if they choose to I don't care but making them do it bothers me for some reason, but there is no logic behind it so I would ignore me.