You can use grass clippings to mulch pretty much anything -- my Dad simply spreads his around flowers, shrubs, whatever, and they all do extremely well. They should be particularly useful around any foliage plants or green veg (cabbages, lettuce) since they are high in nitrogen. Alternatively you could take off the mower collector and just spread the clippings back onto the lawn to feed the worms & the grass, so long as the grass you're cutting isn't too long.