I like the ice cube idea, John.
Dave, I agree that lilacs and peonies struggle here, and I love both. Most of my plants are accustomed to little supplemental watering, however, I HAD to put a few peonies in. HAD to--because I am stubborn (read as "pig-headed") and really wanted them.
Helps that my yard is shaded in the afternoons, otherwise, I am sure the garden would be a lot more sparse than it is right now and the peonies would have fried out long ago.
Glad to know that tomatoes will come back at the end of summer. Put two(!) in this year to try my hand at them and will see what happens.