not sure how big of a file you mean.
it looks like you have to be able to fit the file in RAM.
your best bet might be to turn a File() into a Blob() and use the blob.slice() method to divide the file into chunks.
you may be able to use range headers in ajax requrest to an object URL.
but, the surest way is to just load the whole file into an array buffer and upload chunks of it.