you might be able to use a tiny drop of gasoline- apply a tiny drop of gas to a cloth and then try to gently rub out the sap on the hood. no matter what happens you want to immediately afterwards wash the car. then I suggest you at least wax the hood. this worked for me a long time ago on a honda so I dont know if it will work with the newer bmw paints. a suggestion before you try this is to call your dealer.
ME
ME