I take it Elf is still on a special diet and Smudge no longer needs to build up his weight. May I suggest you designate a specific supervised "dinner time", after which all food will be removed. They will soon adapt. You may recall having to stand back lest you be bowled over by the animals when the timer sounded at 5.45pm every day. One reason for that was Ko-Ko's tendency to be demanding food at all hours of day and night. He soon adapted to the new regime - as will your two cats.