I believe a thin or porous damp towel can be used for evaporative cooling, if it's practical. If they're inside, you might be able to rig something up with a fan and the towel between the dog and the fan. You will, of course, have to pay a humidity tax to accomplish this.
Another thing that I learned living with dogs
in the desert is that dogs really like flavored ice cube treats. Freeze up some savory broth into cubes - they'll go crazy for it and it'll cool them down.