"I'm not talking about submerging here though, just standing in a shallow pool."
Shallow water heats up very quickly and gets hotter than deeper. Unless the water is also circulated, the roots get no oxygen. Swamps that BC grow in are not stagnant. Water moves through them, bringing oxygen. Same cannot be said of a tub of water.
I am well aware of high temperatures. I am in roughly the same growing zone as Dallas, Tex. here in No. Va--USDA Zone 7. I also know about deep south summers and about heat (my folks live in East Tex. I have a lot of relatives on the Gulf Coast). Here in No. Va. we regularly get sustained temps in the high 90s and 100s well into Sept.-- with nighttime temps hovering in the low 80s (nighttime temperatures are a big threat, BTW, as they can interfere with a plant's photosynthetic cycle, or so I've heard). A pool retains heat longer than aerated soil, especially if the soil is watered from above during the day, which brings in not only cooler water, but oxygen as well.
The advice given to me by Gary Marchal
www.cajunbonsai.com (a La. native, but now moved to Ga.) was not to keep BC in standing water, but to augment the soil, using majority organic material to retain water. I've done so for years now. I used to get yellow leaves and early brownout of foliage on BC when I grew them in water. I haven't seen that since moving to more moisture retentive soil.
If your soil is drying out while you're away, move them into a more sheltered spot out of the wind. Morning sun until 1 or so, if possible. It also helps to put wet white T-shirts over the soil surface on really hot days. This not only keeps evaporation from the soil down, but also keeps temperatures on soil surface and pot surfaces a lot cooler...