Rick, it is very easy. I was using a Canon 20d and a 550ex.
I metered for the ambient sunlight which was F11. I placed Ali so that the sun would be a kicker light. I set my flash to output F16 on Ali and had someone hold it out to my left (45 degrees) My camera was set at 1/250 @ F16 to match the exposure of the flash. This in turns darkens down the background as it is one stop more than the ambient.