A barbeque will also work as an oven. Set a cookie sheet on the grill between the burner rocks and the bottom of the part too be cooked. Do not let the part set directly on the cookie sheet though. Suspend the part if possible, using coat hangers or really stiff wire to make a jig. Put the whole thing in the barbeque and cook slowly on low heat, checking often untill well done.
Never, ever use the barbeque for cooking food afterwards, ever!!!