When Otacon gives you the ketchup, escape without using it. Go anywhere outside where there are guards. Lay down in the snow and select the ketchup. Solid Snake will immediately spill the ketchup. Wait until a guard walks by and sees you. He will freak out and go for help. Hide somewhere where you can still see the ketchup stain. Eventually the guard return with some friends. He will show them the ketchup. One of them will get mad and shoot him.