104 code (or latter) + moving the slot back.
There are threads on Pinside with pictures.
Quoted from LesManley:
Unfortunately I don't think the Gene's head fix is going to be the magic elixir that makes it earn more. 90% of the players don't even realize it is an issue even when they can't lock a ball. They just think they didn't hit the shot solid enough.
The "easy" fun of KISS is that multiball, so if you can't easily achieve it, it probably would not draw players back.
Not every game earns in every location, but most the ops I know have a dozen KISS and they are really earning well.
Mix the games up and find out how much money is in that room.