Once you have seared EACH side, turn off one burner and turn the remaining burners to medium for indirect cooking. For a 3 burner system, turn off the middle burner and leave the outside burners on medium. For a 4 burner system, turn off the middle 2 burners and leave the outside 2 on, you get the point. Place the roast beef over the 'off' burners.
Important Note: Check out this
grilling tip if you use your grill's lid thermometer as an indication of your cooking temperature. Here's a hint, it's lying to you...