The short answer is you're going to pat them on with your hand. Here's how. First, start with a cake with frosting that hasn't yet hardened or set. Then be sure that your chocolate shavings that are pretty cold. Although you'll be working quickly, you don't want them to melt in your hand. Place strips of parchment or waxed paper around your cake so you can catch the chocolate shavings that don't stick to the sides. Then, fill the cup of your hand with chocolate shavings and pat it onto the side of the cake. Press lightly, but enough to get them to stick onto the cake. Be careful not to smudge the frosting. So the more shavings you can fit into your hand, the better it will be. If you can tilt the cake a little bit, that will help. But you might not be able to. You'll get there, just keep filling up your hand and carefully patting the chocolate shavings onto the cake. Use a pastry brush to brush off the fallen chocolate shavings, then remove the strips of parchment or waxed paper.