Place a dot of chocolate on a serving plate large enough to accommodate a 3-by-9-inch Styrofoam cone; place the cone on top of the chocolate and let stand until set, about 10 minutes. Using an offset spatula, cover the cone in the melted chocolate; refrigerate until firm, about 15 minutes.
Break a toothpick in half and insert it, broken-end first, into the bottom edge of the cone. Place a frozen cream puff on the end of the toothpick. Continue this process around the bottom edge of the cone, placing cream puffs so that they touch. Continue placing cream puffs in this manner as you travel up the cone, occasionally placing a macaron on a toothpick instead of a cream puff. At the very top of the cone, insert a toothpick upright and place a macaron on top, also upright. Dust the centerpiece with confectioners' sugar using a sieve. Tuck flowers among the cream puffs and macarons. Allow the assembled croquembouche to come to room temperature and serve.