Posting to web service with Multipart MIME

[bboren]

Does anyone have experience in posting to an API that accepts Multipart MIME? 

Trying to determine the feasibility of connecting to an application.  It needs us to submit an XML payload and then one or more documents as base64 encoded via a multipart MIME post.

I assume the SDK will be needed but wondering if anyone has done similar to confirm it is possible.

Thanks!