Is there any thing else I can do to prevent freezing radiator

Just got truck from friend passing away. No antifreeze in radiator only cap is on reserve. I tried to drain from underneath spout but it broke off in closed position slid metal ring clap off of hose line but it won't budge now it's getting dark outside and it's going to freeze. I left cap off for expanding water to go to. Is there any thing else I can do to prevent freezing radiator and messing up engine? Would one of those mechanics dual stand up lamp bring out enough heat if I place it over it?