Extending dashboards filters

[ela]

I would like to a dashboard by setting a value of a filter. Here are my dashboards:

- dashboard: summary_report
  title: Summary Report
  layout: newspaper
  extension: required
  - elements:
    - title: Blab
      ...
      listen:
        Filter: some_field
  - name: Channel
    title: Channel
      type: field_filter
      allow_multiple_values: false
      required: false
      explore: explore
      field: some_field
      model: app
      listens_to_filters: []

- dashboard: specific_report
  title: Specific Report
  extends: summary_report
  - elements:
    - title: Another element
      ...
      listen:
        Filter: some_field
  - name: Channel
    title: Channel
      (here I would like to extend Channel filter)
      default_value: DEFAULT_VALUE

Any idea how I can do this? I don’t know where to put ${EXTENDED} in this case