While trying to think of a word or phrase that would fit our welcome "guest" 's request, I encountered in spellingbee list
word "holophrastic" defined as "expressing a complex of ideas in a single word". T think the example the Scripps-Howard people gave is very dubious:
"Holophrastic utternaces are one of the first stages in childrens's acquistion of speech."

Let's get back to "guest"'s request. Ephemeral means of short duration, but not short enough. He wants "Take it or leave it" in one word if possible. I think it will have to be a short phrase.