JSON Configuration for Grid Column Edit: Dropdown List Using Service Data

I am trying to configure a grid widget to editable via a dropdown list in one or more columns.

I have reviewed the documentation here and here. 
Both documents that detail JSON configuration and dropdown lists indicate statically defining the dropdown list selections in the JSON configuration directly (ie

"dropdownConfiguration": {"items": ["Active", "Parked", "Undergoing Maintenance"]}

Due to the potential size and expected change over time for the list of selections I would like to define the dropdown list via a service rather than statically defined in the JSON configuration.

I would appreciate some guidance on how to define a data source to be used for the dropdown list