Getting closer and lower like everyone is saying should get you there. Distortion is still going to be a bit different in your shots than in a lot of the commercial shots you see because of the fovcf of your camera. With a 1.6 crop body you don't get the same drastic distortion that you would see on a ff or on a medium to large format camera that i suspect a lot of commercial shots are taken with. Thats not to say however that you can't get some really neat distortion from your setup, just experiment away. The lower you get, the more you can angle your camera up, almost getting a bit of a worms eye view perspective and that should help with the distortion as well.
Rebel xt w/ bg-e3 grip, 70-200 f/4L, Canon 50 f/1.8, Tamron 17-50 f/2.8, speedlight 220ex, currently accepting donations for ABR800. 