How to send multipart/mixed rest request to upload files

I also am attempting something very similar to this. I need to send a multipart/mixed POST with two parts: binary object meta-data, content-type application/json, followed by the binary object data itself (content-type dependent upon the file: image, document, whatever).

There seems another similar post on this topic, with no response. Does this mean that SoapUI can't do this?

Thanks.