How to populate a multi-select Dropdown question with names from a Directory list

I'm trying to set up a survey question that lists around 10-15 names of people. At the moment I've just pasted them directly in using the usual edit functionality. However, that list of names may change frequently and what we'd like to be able to do is link the question to names in a Directory list so that when we update the names in that Directory list, the names in the dropdown question in the survey automatically update. Is there a way to do this?
Thanks