In microwavable bowl, microwave candy melts and shortening uncovered on Medium (50%) 2 minutes, then in 15-second intervals, until melted; stir until smooth. Dip tip of 1 lollipop stick about 1/2 inch into melted candy and insert stick into 1 cake ball no more than halfway. Repeat. Return cake pops to cookie sheet. Refrigerate 5 minutes. Remove from refrigerator a few at a time. Dip each cake ball into melted candy to cover; tap off excess. Immediately dip top in walnuts, pressing to adhere. Poke opposite end of stick into foam block. Let stand until set.