Try this method; when the bars are chilled, turn them out of the pan, cut to desired shape -diamonds or squares or what ever, arrange them on a wire rack and pour your chocolate over the individual pieces. Then chill. I usually line the buttered pan with waxed paper or parchment cut long enough to hang over the pan on opposite ends. Butter or grease the paper and proceed as usual. When it time to take the bars out of your pan just lift by the paper. Foil works also. Hope these ideas will help. Let me know how it works out for you !