Try to find "teamaker" hops. A variety bred specifically for their lack of alpha acids. For use in tea's, medicinals (SOUP!)

good luck... definitely add them late, ever made hop tea? you could try some timing/hop combinations and see if you find something that might compliment the soup. Or steep some tea for a short period and strain and mix it with the soup, so that you dont have hop vegetable matter in there, and so the AA's stop bittering...