Any pointers on how to accomplish this would be greatly appreciated!
Did you ever figure this out? I just had a questionnaire dropped on my desk where this ability would be useful.
Under Validation you have a AUTO SUGGEST that will work dynamically. You can require responses on on the list you have uploaded or allow them to enter something else. You can enter a really long list too.
Something else you might want to use is the HTML Placeholder under Layout to shadow what they should be entering or how they should enter a field. Makes your survey look very professional.