How to add request body to swagger docs without specifying it as a method parameter?

Question

I have a .net core 2.0 Web API that uses Swashbuckle to generate the swagger documentation. There is one POST endpoint I need to specify the request body in the swagger documentation without specifying it as a [FromBody] method parameter of the controller. Can't specify this as a method parameter since the request body changes depending on the order type. I just want to specify the BaseOrderModel as the request model in swagger documentation. How should I accomplish this?

The following code snippet will give some understanding of my code.

// Contoller
[HttpPost]
[Route("checkout")]
[ProducesResponseType(typeof(CheckoutOrderDto), (int)HttpStatusCode.Created)]
public async Task<IActionResult> CheckoutOrderAsync([FromQuery] OrderType type)
{

    BaseOrderModel? order;

    switch (type)
    {
        case OrderType.Pickup:
            // Deserialize to PickupOrder model
            break;
        case OrderType.Delivery:
            // Deserialize to DeliveryOrder model
            break;
        case OrderType.UberEats:
            // Deserialize to UberEats model
            break;
        default:
            return BadRequest("Invalid order type");
    }

    // Omitted rest of method for brevity
}

// Enum
public enum OrderType
{
    Pickup,
    Delivery,
    UberEats
}

// Models
public abstract class BaseOrderModel
{
    // Omitted props for brevity
}

public class PickupOrder : BaseOrderModel
{
    // Omitted props for brevity
}

public class DeliveryOrder : BaseOrderModel
{
    // Omitted props for brevity
}

public class UberEats : BaseOrderModel
{
    // Omitted props for brevity
}