How to export MarianMT to ONNX with output_attentions=True?

I’m trying to understand how to export MarianMT to the ONNX format with the output_attentions parameter set to true. The Huggingface docs provide the following example here detailing how to achieve this in the case of Whisper:

from optimum.exporters.onnx import main_export
from optimum.exporters.onnx.model_configs import WhisperOnnxConfig
from transformers import AutoConfig

from optimum.exporters.onnx.base import ConfigBehavior
from typing import Dict

class CustomWhisperOnnxConfig(WhisperOnnxConfig):
    def outputs(self) -> Dict[str, Dict[int, str]]:
        common_outputs = super().outputs

        if self._behavior is ConfigBehavior.ENCODER:
            for i in range(self._config.encoder_layers):
                common_outputs[f"encoder_attentions.{i}"] = {0: "batch_size"}
        elif self._behavior is ConfigBehavior.DECODER:
            for i in range(self._config.decoder_layers):
                common_outputs[f"decoder_attentions.{i}"] = {
                    0: "batch_size",
                    2: "decoder_sequence_length",
                    3: "past_decoder_sequence_length + 1"
            for i in range(self._config.decoder_layers):
                common_outputs[f"cross_attentions.{i}"] = {
                    0: "batch_size",
                    2: "decoder_sequence_length",
                    3: "encoder_sequence_length_out"

        return common_outputs

    def torch_to_onnx_output_map(self):
        if self._behavior is ConfigBehavior.ENCODER:
            # The encoder export uses WhisperEncoder that returns the key "attentions"
            return {"attentions": "encoder_attentions"}
            return {}

model_id = "openai/whisper-tiny.en"
config = AutoConfig.from_pretrained(model_id)

custom_whisper_onnx_config = CustomWhisperOnnxConfig(

encoder_config = custom_whisper_onnx_config.with_behavior("encoder")
decoder_config = custom_whisper_onnx_config.with_behavior("decoder", use_past=False)
decoder_with_past_config = custom_whisper_onnx_config.with_behavior("decoder", use_past=True)

    "encoder_model": encoder_config,
    "decoder_model": decoder_config,
    "decoder_with_past_model": decoder_with_past_config,

    model_kwargs={"output_attentions": True},

And I’ve tried naively swapping out the Whisper ONNX config for the MarianMT equivalent, but doing so results in the error:

ValueError: You have to specify either decoder_input_ids or decoder_inputs_embeds

which I’m not sure how to interpret. I’m wondering what I would need to change in order to make the example suitable for exporting a model like MarianMT, and more generally, what a roadmap for developing the understanding to answer these kinds of questions myself might look like?