Could you not meter off a black white or greycard using a reflected value? Remember all Meters only give values for medium gray.
You would visually have to asses the light and highlights to determine if the highlights would blow out. Shadows will fall in place. I know this is opposite standard zone practice but not using a spot meter here so the inverse is required.
Another thought. If you use an ev mode you would be measuring average light reflected or incident. Therefore you would know how far to deviate from a standard such as "sunny 16". Again with practice one should be able to see the range of light within the scene.
When in doubt, use Polaroid. But it may not have same lattitude as your film.