How to use a custom jsonDecodeCallback with BackgroundTransformer

[lars-hl-knowit]

Hello, in our Flutter project, we've set the transformer for our Dio client like this:
dio.transformer = DefaultTransformer( jsonDecodeCallback: (body) { final transformedBody = _convertLongIntsToString(body); return json.decode(transformedBody); }, );

After updating the Flutter Dio package, DefaultTransformer is now deprecated, and one is advised to use BackgroundTransformer instead. But BackgroundTransformer does not accept a custom jsonDecodeCallback function. We need this, because the data our app interacts with uses numbers for IDs which are so long that when the app is built for Web, and converted to java script, these IDs are misrepresented. So we convert them to strings with our custom jsonDecodeCallback function.

So, is there a way to achieve the same functionality using the now recommended BackgroundTransformer instead of the deprecated DefaultTransformer?