You dont want to add data directly in the console as if the computer object is deleted you lose that data. The best way without Data Analytics is to create an entry in the devices registry that you can bring back as custom data in LDMS. You can then query on this field.
The hard part will be working out how to query AD from the client to obtain the department and then write this to the registry.
I would take a look at Data Analytics as this will give you what you want straight away plus much more functionality and enhanced inventory info.