How to stream R2 file inside FormData in fetch request body?

export default {
    async fetch(request: Request, env: Env) {
        const key = 'some_video.mp4';

        const object = await env.MY_R2_BUCKET.get(key);

        const form = new FormData();

        const fileStream = object!.body;
        const fileBlob = await object!.blob();

        form.set('some_text_field', 'value here');
        // I want to use the `fileStream` here instead of `fileBlob`
        form.set('video', fileBlob, 'video.mp4');

        const resp = await fetch('https://api.example.com/some/endpoint', {
            method: 'POST',
            body: form,
        });

        console.log(await resp.text());
    },
};