I think someone suggested a 3 gallon container with pebbles...(it's been a long day

). That's an excellent suggestion. Point of fact, a pair of 5 gallon buckets filled with rocks -- for the bees to crawl on -- would give you even more time.
If rocks are hard to come by, stack a layer or two of standing bricks in your 5 gal buckets. You can fill the water right up to about half an inch below the top of the brick and your 'invaders' should have enough to land on.
I would imagine that this situation will probably go away at some point in the near future. Nature has a way of balancing things out. However, if the problem returns next year, then I would start looking around. There's got to be a bee keeper close by who isn't doing a very good job of caring for their bees.
Keep us posted and good luck!