Ouch! Hateful little creatures
The aerosols won't work on in-ground nests for the reasons you pointed out. You need gravity to pull it down, but aeros are lighter than air. The sevin dust is excellent on all bees. Instead of using the dust as dust, mix it with water in a bucket or jug, and pour it into the holes. Gravity and the weight of the water will take it down nicely. You could then put the dust at the outside of the hole for good measure. Sometimes you need a make a second application even with the liquid. A gallon of mixture should be plenty. I don't know what to tell you about dust to water ratio-we use liquid concentrates mixed with water, but Sevin is terrific on bees. We would have no other use for Sevin, so we don't carry it. It won't hurt the grass, so mix it generously.