in addition to what Chris said, I used the AF illuminator (the little plastic piece that can be put infront of your flash, I think that is what it is called) and placed it infront of it.
But reflectors are a must to get a good shot with a wide angle. Most flash units handle starting at 24mm so in order for the light to be spread evenly you need to point your flash away from your subject and bounce it off a reflector, ceiling or a wall to disperse the light as much as possible.
here are some example shots Ive taken with a wide angle with this technique
