Although I haven't fully tested it the following method should work (at least to get you to a starting point):
1. Take a reading at grade 0 of a highlight area. This is your grade 0 exposure - write it down. Take a second reading of a shadow area, and note which grey scale LED lights up. This represents how the shadows will look following the grade 0 exposure.
2. Clear the measurements, switch to grade 5, and repeat the reading of the shadow area. Write down the indicated exposure time. This represents the exposure at grade 5 which would produce the same shadow density as the grade 0 exposure.
3. Increase the exposure until the LED reaches the far right (black) end of the scale. Note the indicated exposure, and subtract from it the time you wrote down in step 2. The result is your grade 5 exposure.
Let us know how you get on!