Condition for adding data parameters

Configuration
1

I am trying to configure multiple Aqara Cube actions via a single script. It should be possible to increase the volume, decrease the volume, or reset the volume to a fixed value.

Currently this works like this:

Automation:

[...]
action:
  - service: script.play_music
    data_template:
      entity_id: media_player.google_nest_hub
      command: |
        {% if (trigger.event.data.command == 'rotate_right') %}
          volume_up
        {% elif (trigger.event.data.command == 'rotate_left') %}
          volume_down
        {% else %}
          volume_set
        {% endif %}
      volume_level: 0.4

Script:

choose:
  - conditions:
      - condition: template
        value_template: '{{ command == "volume_up" }}'
    sequence:
      - service: media_player.volume_up
        data_template:
          entity_id: '{{ entity_id }}'
  - conditions:
      - condition: template
        value_template: '{{ command == "volume_down" }}'
    sequence:
      - service: media_player.volume_down
        data_template:
          entity_id: '{{ entity_id }}'
default:
  - service: media_player.volume_set
    data_template:
      volume_level: '{{ volume_level }}'
      entity_id: '{{ entity_id }}'

I would like to simplify this by putting all options into a single condition. However, this fails because media_player.volume_set needs the volume_level parameter, but media_player.volume_up won’t accept it:

voluptuous.error.MultipleInvalid: extra keys not allowed @ data['volume_level']

Is there a way to skip adding the volume_level using a condition?