How to test amazon s3 in sandbox environment with AmazonS3Client

How do you test S3 in a sandbox environment when your code uses an AmazonS3Client?

IAmazonS3 amazonS3Client =
           Amazon.AWSClientFactory.CreateAmazonS3Client(s3AccessKey, s3SecretKey, config);

var request = new PutObjectRequest()
{
    BucketName = "bucketname",
    Key = "filename",
    ContentType = "application/json",
    ContentBody = "body"
};

amazonS3Client.PutObject(request);

I've tried S3Ninja and FakeS3 but they didn't work, which leads me to believe that an AmazonS3Client doesn't behave like a normal rest client.

The only solution I can think of is to convert the code to use a rest client and manually build the requests and headers just so that I can use S3Ninja or FakeS3.