How to make ObjectVar with grayed out choices?

[llamafilm]

In a custom script, I have a variable like this:

    switch_interface = ObjectVar(
        model=Interface,
        required=False,
        query_params={'device_id': '$switch', 'occupied': False}
    )

This lets you choose from available interfaces only.

I'd like to make the dropdown list show all interfaces, with the occupied ones grayed out, not selectable, as it does on the /dcim/cables/add page like this:

Is this possible? It would help to avoid confusion sometimes if the user expects to see more interfaces and doesn't realize why they are missing.