It's best to buy yourself a trivet which looks like a cake rack but thicker.
Place a doubled over sheet of foil on the grates leaving at least 1-2 inches all way round the edges from the sides of the grate, with a knife, make a series of slits in the foil between the grillbars so any fats and oils can drip down to the tray underneath, place the trivet in the middle of the foil and place chicken ontop.Grill with control 2 notches down from Hi, this seems to be the sweet spot for grilling or roasting, if you want lower temps, just turn down as low as possible.
This method allows the hot air inside the Q circulate around and under the food giving you even cooking.
You could also place the trivet inside a thick foil tray if you wish to retain some juices to use for basting etc; as long as the chicken has air underneath.
Hope this helps.
Cheers
Davo