Is there a way to create a Cascading ComboBox populated by an SQL/SDK query to a table? Referenced Lists too hard to maintain.

Question

Background:
I’m looking for an alternative to using referenced Enum (aka Lists) for “dropdowns” (aka “ComboBoxes”) in the forms.
The reason for looking for an alternative mechanism for drop-downs was that using referenced Enums
 ran into issues when the List items in the enum were to be updated:
The SCSM Console refuses to allow for the deletion of the referenced 
Enum MP when there are other MPs referring to it.
The SCSM Console doesn’t allow the editing of a sealed Enum MP’s List items.
One has to hand-add new list items to the Enum MP’s XML.
Importing that new Enum MP over the old one causes views to not show data for the changed Enum.
The Customer wants the dropdown choices to be dynamically updated.
The Customer also wants this to be user-friendly “for the masses”, meaning that hand-editing XML and tinkering with the SCSM Console is undesirable.
We had enumeration lists with hundreds of choices, making hand-entry, using the SCSM Console, inordinately lengthy, error prone, and, frankly, tedious.
What I’m looking for:
The deeper requirements implied in these three Use Cases below are:
The system has to be easily maintainable.
The system has to reflect the latest changes in data.
The system has to be usable by “the masses”.
Large sets [200+]  of choices have to be machine importable.
 [Note: one reason why enums are not desirable is that we have had
hundreds of choices to add and a manual approach was not feasible]
Not as a prescription for a solution, but as a way of showing what I am looking for through an example-that-says-more-than-a-thousand-words: I want to implement the Service Manager usage-equivalent of a
 “Cascading Dropdown” (aka “Cascading ComboBoxes”) instead of using Enums. It doesn’t have to use
Cascading Dropdowns but allow for the back-end ease-of-use that comes with it.
Use Cases:
Use Case 01:  A User wants to edit the contents of a Windows Computer CI record.
Say that I want to change the field Business Unit and its associated field
Customer
You pick one element from a list of Business Unit choices.
The act of clicking on that field triggers a SQL search through a table of all current customers and populates the dropdown for the field
Business Unit.
Say, for the sake of an example, you pick the Business Unit “Accenture AO”.
The act of chosing “Accenture AO” triggers another SQL search through a table to find all
 Customer values that belong to the Business Unit “Accenture AO” and that filtered set is used to populate the dropdown for
Customer.
The user chooses “Planet Express”.
The act of chosing “Planet Express” triggers a final SQL search through a table to find what the two-letter code is for “Accenture AO” + “Planet Express”, say “PE”. That value is used to set a
hidden field.
Use Case 02: Maintaining the tables used to populate Business Unit and
Customer lists
Say I’m an Admin who wants to update Business Unit and Customer
lists as there have been the creation of a new Business Unit “Accenture Galactic” and there have been new Customers ”Klingon Karrier”, “Romulan Relaxair”, and “Federation Fun” and, say,
two-hundred other Customers, with their two-letter codes “KK”,”RR”,”FF”…etc…etc..etc… respectively.
I open a table editor for Business Unit and Customers.
I have, say a CSV that has the Business Unit, Customer, and Code field and 200+ records
I import using some automated mechanism the 200+ records.
Use Case 01-B: A user immediately has their choices updated.
Say that I want to change the field Business Unit and its associated field
Customer
You pick one element from a list of Business Unit choices.
The act of clicking on that field triggers a SQL search through a table of all current customers and populates the dropdown for the field
Business Unit.
Say, for the sake of an example, you pick the Business Unit “Accenture Galactic”.
The act of chosing “Accenture Galactic” triggers another SQL search through a table to find all
 Customer values that belong to the Business Unit “Accenture Galactic” and that filtered set is used to populate the dropdown for
Customer.
The user chooses “Federation Fun”.
The act of chosing “Federation Fun” triggers a final SQL search through a table to find what the two-letter code is for “Accenture Galactic” + “Federation Fun”, say “PE”. That value is used to set a
hidden field: “FF”

Answer 1

consider
http://blog.scsmsolutions.com/2011/08/create-custom-user-control-for-scsm-2010/ and http://social.technet.microsoft.com/Forums/en-US/09813153-a4d0-4bce-8d28-3ccc63bd72a1/resources-for-adding-custom-wpf-controls-to-service-manager-forms?forum=customization
As for the Data Typing, the class property would be a String type, which maps to NVARCHAR in SQL, so any unicode characters, including XML (i'd recommend keeping it below 4000 for performance reasons). look to how the UserInput control works in Service Requests. 
I would recommend a class extension woth a single string property to store the data on the windows computer class, and a separate stand-alone class to store your "options". no relationship should be implied.