“What if we use the ‘‘custom audiences’’ thingy, but just populate it with 299 deceased people and 1 person whom we really need to show this ad to?”
LinkedIn requires at least 300 people in a custom audience, supposedly so nobody can aim an ad at one person. Two Ukrainian founders in London padded the list with 299 names from obituaries and served an ad to exactly one living target. He liked it. LinkedIn’s privacy floor is a head count, and the dead count.