How can I use Relay GraphQL client to upload the files

Question

I have the following use case:

I have an Apollo compatible file (form-multipart) GraphQL resolver for handling files (in the backend). The React App is using the Relay client.

How can I make an upload mutation using the Relay client?

The app is already using the latest Relay (v4.0).

I would like to avoid:

• setting up Apollo client in the app (just to make the file upload)
• fall back to REST and separate one request into two (graphql mutation + REST file upload).