Append data to streaming response

I am creating an application built on top of OpenAI’s chatGPT. I am using their API’s streaming option to allow streaming. In my Remix (nodejs) backend, I simply pipe the response through to the client:

const theresponse:any = await openai.createChatCompletion(...);
return new Response(theresponse.body, { headers: headers  });

I would like to append some data to the response sent to the client, but I am unsure how to do it. Everything I try breaks the stream. How does it work with streaming?