First, make sure you have the bomb and a vehicle that you can drive. Then, have a friend drive the truck, robot, etc. up to the bomb point. Start to place the bomb, but move so you can place it on the vehicle (which should be directly on top of the target. Have your friend drive away and park the vehicle somewhere hidden. Run away and the CT's will not know what is happening. You can also do this when playing with bots, but it will take longer.