I don't believe you can. The CDU is simply a data entry component. The NZ computer is the brains to the system itself. The primary components of the system like I said previously are at minimum the CDU (Control Display Unit) and NZ (Navigational Computer) and a DL (Data Loader). The newer systems (incorporating the CDU-820) are also capable of Video (up to 6 cameras I believe) and also graphics (AIRSHOW, ONEVIEW, Terrain Telelink). So basically to answer the question is all of the components make up the FMZ series system. So you would have to have the minimum components (ie NZ,DL,CDU) to have the FMZ system. Can't have one with the rest.
By far of the FMS systems that I have used UNS, GNS-XLS, FMZ-2000...the Honeywell FMZ-2000 is by far the easiest(most logical) and the most powerful one available. I have never used the Collins units but I have heard that they are not as user friendly as the Honeywell system is. Just my $.02.