Hum, I don't know if the light levels needed to grow the greens would bother the worms or if having the surface uncovered so that the greens could grow would cause faster drying and require some additional watering.

In any case it is worth a try and you can let us know how it works out. I know I get tons of musk mellon seeds sprouting in my worm bin so it should work for lettuce.

sounds like a cool experiment.

Here is a link that might be useful: My worm bin

Given the right amounts of light and moisture it should work fine. I do the same thing in my garden/worm farm all the time. Plantnfool.