try using butter flavored shortening instead of butter in the icing. i actually don't like the way it tastes with butter in it so i have always used shortening in the wilton icing recipe and then adding 1/2 tsp of butter flavor. even doing half butter and half shortening should help it hold up instead of melting.
if you are making something that will have flowers or something fancy on them, make the flowers ahead of time and let them dry. it's always been less frustrating to have the flowers act up if i make them ahead of time than on a busy day when i'm icing and decorating the final product. not much help now, but something to keep in mind next time