In backlight, you can use "The Duplex Method" as described in Dunn and Wakefield's Exposure Manual(sadly out of print), in which you point the dome at the Sun, note the reading, then from the subject at the camera, and average the two readings, this works in any light, front side or backlight.
To be accurate, you don't point the dome at the sun. You hold it parallel to the earth, but in the direction of the sun.
