I have written about using the reverse sear technique a good bit but someone recently asked me how to do that on a gas grill. It's really not much different - start with a slow roast at low temperatures and then finish over a high temp sear.
I did a reverse sear recently for a post over at Char-Broil Live when I made these Reverse Seared Strip Steaks with an Oyster Mushroom and Asparagus Stir Fry.
Here is the basic setup that I used on my Char-Broil Gourmet TRU-Infrared grill.
This is the set up at the beginning - only the left burner was on, so the steaks roast with low indirect heat. When they hit 5 degrees less than my desired final internal temp - I remove them, turn up the heat, and let the steaks rest until the internal temp stops rising. Then it is back on the grill for a quick sear.
For full details and the recipe, hop on over to my post at Char-Broil Live.