How to create lookup field that only list unique records

How to create lookup field that only list unique records

Hi, I have several single line fields in my form of which most have duplicate records, but I need the user to go through a 4 step process of selecting from a lookup list, then the next 3 fields will be a dynamic pick-list based on previous selections, but I don't want the duplicates to show up in any of these drop downs...

I've tried to configure the lookup field with a distinct aggregate record function, but it either doesn't work or I'm doing it wrong. 

 Is there a better way?

Cheers
Eric