So I guess what Christian bakers need to do when asked to bake cakes for homosexual "weddings" is to bake a cake but not decorate or frost it. Instead, give them the baked cake, the frosting and the decorations (make them buy two sets of wedding toppers so they can get the two grooms or two brides) and let them decorate it as they choose.
The same thing for Christian florists. Sell them the flowers, but have them delivered in big boxes. Allow the customer to arrange and place the flowers as they see fit.