We keep it simple and mix a dollup of dish soap with a cup or two of water in a spray bottle, slosh it around, and spray directly to the infested area. Some people add vegetable oil to the mixture, but in our experience, it hasn't been necessary. We think that if you are vigilant enough when the flowers are buds than the aphids will be gone by the time they bloom, meaning the petals will be free of both the bugs and the less-than-appetizing soap mixture. Planting anything that attracts ladybugs nearby (spearmint, Queen Anne's lace) might also help, as they prey on aphids. Any other suggestions?