For even more fun, start with that brush with a stroke width of zero and a transparency of around 30%. Draw a path that meanders upward in a lazy sort of back and forth. Use a medium gray.
Now animate the width at the end of 60 or so frames so that the path tapers from start to finish, and ends ridiculously wide (you can't make it too wide). Finally, animate the stroke exposure so that it starts at the bottom and goes to the top.
Dupe this layer two or three times with various colors and transparencies and you'll have a pretty good genie from the lamp smoke effect.