Upload file to Amazon S3 bucket from .Net Portable Class Library?

Question

I'm using a PCL in a cross-platform mobile .Net (Xamarin) project. When I try to install the Amazon SDK via Nuget into my PCL it fails.

All I need to do is upload some photos to my S3 bucket. What is the simplest way to accomplish this, either by using some other PCL-friendly library, or just via the .net http library?