PDF Services Upload from Form-Data

Hi all. Looking for assistance uploading via the PDF Services API. The docs are pretty sparse and don't actually include the PUT method. I'm trying to build an integration that can upload a PDF so I can then convert that to PPTX. I've got this working locally with the Node SDK but I can't use that because the result from the export operation isn't what I need (and I can't fork the SDK to make the necessary changes so that would work).

I'm looking to use the following flow:

1.  Generate asset upload URI
2.  Fetch the PDF from an S3 bucket source as stream
3.  Upload to upload URI via the stream from step 2. 

Question:

How can I upload to an upload URI using form-data / a stream instead of needing to passing binary data from a local source? Any examples of this would be greatly appreciated!