I’m not sure I understand your anecdote. I had actually never heard of “stone soup” by grandparent but I found it in Wikipedia as this story: https://en.m.wikipedia.org/wiki/Stone_Soup

My interpretation of grandparent as applied onto that story was that some of their colleagues had some local solutions that were part of the puzzle and OP purposefully created some ancillary solution (the “stone soup”) to get them to contribute to the bigger picture. But perhaps I’m seeing this entirely wrong?