How can I transform Fixed Collection output to match an API's expected format in a declarative custom node?

Transforming Fixed Collection Data in Declarative Nodes

I'm developing a custom node using the declarative style and need to modify the data format so that my API endpoint receives it as expected. My current setup uses a Fixed Collection defined as follows:

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{
    displayName: 'Item Test',
    name: 'itemTest',
    placeholder: 'Add Item Test',
    type: 'fixedCollection',
    default: '',
    typeOptions: {
        multipleValues: true,
    },
    options: [
        {
            name: 'itemValues',
            displayName: 'Item',
            values: [
                {
                    displayName: 'Name',
                    name: 'name',
                    type: 'string',
                    default: 'Name of the Item',
                },
                {
                    displayName: 'Quantity',
                    name: 'quantity',
                    type: 'number',
                    default: '',
                    description: 'Item quantity',
                }
            ],
        }
    ],
}

This produces the following output from the node:

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{
  "itemTest": {
    "itemValues": [
      { "name": "Item 1", "quantity": 1 },
      { "name": "Item 2", "quantity": 2 }
    ]
  }
}

However, the API expects the data to be formatted like this:

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{
  "items": [
    { "name": "Item 1", "quantity": 1 },
    { "name": "Item 2", "quantity": 2 }
  ]
}

Is there a way to perform this structural transformation in declarative mode, or must I switch to programmatic mode? Any guidance or best practices would be very helpful!

Thanks!