There are two things you can do to prevent your cones from getting mushy. The first thing is to make sure that when you wash your fruit, let it dry on a clean kitchen dish towel or a drying mat.  My second tip to is not fill the waffle cones until you are ready to serve them up. Another idea you can do is to set up a Fruit Cup station and let your guests or family fill up their own bowls when they are ready to eat the fruit.