I always used to make a point of saying, "I'll see you later, I'll be back after work". I don't actually use the word goodbye (no I know that wasn't the question, just offering), but i always let them know that I am going and will be back.
My DH reckons I shouldn't, especially with velcro man DS as it makes it worse, but then he's hysterical when I get back because he's figured out I've gone and he doesn't have any reassurance I'll be back.