After having no success with diatomaceous earth or honey, I decided to try garlic.
I have been using "Mosquito Barrier" in my garden for two years now. It's a super-concentrated all-natural garlic liquid that you mix with water and spray. It repels mosquitoes and ticks but also many other garden pests and prevents them from munching on the leaves and veggies.
http://www.mosquitobarrier.com/ (They also make a milder form called "Garlic Barrier" but I've found the MB is the most effective for my needs.)
MB doesn't repel bees, but I was desperate and hoped wasps might feel differently, especially if I didn't dilute it at all.
So, about five nights ago, I poured MB full-strength into the two holes. The next day, many of the wasps were staggering around the edge of the hole, walking instead of flying and, I think, getting a good bit of the diatomaceous earth that was still around on them in the process. By the evening one of the holes had quite a few dead wasps outside it.
That night, I poured a little more MB down each hole.
The next afternoon, I saw that they had abandoned one of the holes and excavated a new hole further into the lawn. So, I marked it with a rag tossed from a distance near, but not covering, the hole and poured MB into it that night after dark. I also sprinkled some diatomaceous earth on top of it.
Next day, some wasps were still flying in and out of the hole but some were doing the weird walking-not-flying routine. I poured a little more MB in the new hole that night.
Friday we were out at a party, so no wasp-eradicating work was performed.
Saturday morning, lo and behold, some creature had dug up part of the nest and removed a big chunk of the comb.
And this morning there was even more of the nest dug up by the new hole and comb scattered about. Haven't seen any wasps today. I've got a couple of large holes to fill in (in a few days when I am sure they are gone), but I'm happy that an all-natural and organic approach actually worked.
Odd that the nocturnal raider didn't show any interest when there was sweet honey poured all over the lawn (which was the whole point of the honey-- to attract a nest-digging visitor.) But I guess even skunks and raccoons can't resist a delicious garlicky meal!