MQTT optimistic flag with Shelly Discovery

Hello. I’m trying to setup Shelly 2.5 devices as roller shutters using MQTT. They are discovered using the Shellies Discovery python script. The issue is that I need to set the optimistic=true flag because my rollers can’t provide positioning, so they’re always closed in HASS.

How do I do this with the new YAMLless MQTT integration and the discovery script?

Shellies Discovery automations:

- id: shellies_announce
  alias: 'Shellies Announce'
  trigger:
    - platform: homeassistant
      event: start
    - platform: time_pattern
      hours: "/1" # Modifying this if you are using Shelly Motion can drain your device's battery quickly.
  action:
    service: mqtt.publish
    data:
      topic: shellies/command
      payload: announce

- id: shellies_discovery
  alias: 'Shellies Discovery'
  mode: queued
  max: 999
  trigger:
    platform: mqtt
    topic: shellies/announce
  action:
    service: python_script.shellies_discovery
    data:
      id: '{{ trigger.payload_json.id }}'
      mac: '{{ trigger.payload_json.mac }}'
      fw_ver: '{{ trigger.payload_json.fw_ver }}'
      model: '{{ trigger.payload_json.model | default }}'
      mode: '{{ trigger.payload_json.mode | default }}'
      host: '{{ trigger.payload_json.ip }}'
      ignore_device_model: true
      qos: 2
      shutters-livingroom-left:
        device_name: "Shutters Livingroom Left"
        roller-0-name: "Shutters Livingroom Left Roller"
        roller-0-class: "shutter"
    ...