The following code snippet will allow you to configure an AWS SQS queue for long polling using the ReceiveMessageWaitTimeSeconds attribute. For more information about Amazon long polling, see here:

http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-long-polling.html

// 5. Set Queue attributes
// The API Version 2012-11-05 of Amazon SQS provides support for long polling. (.net sdk v2)
// In the AWS console, you can verify in "Receive Message Wait Time" value of the queue
SetQueueAttributesRequest setQueueAttributesRequest = new SetQueueAttributesRequest();
List<Amazon.SQS.Model.Attribute> attributes = new List<Amazon.SQS.Model.Attribute>();
Amazon.SQS.Model.Attribute attribute = new Amazon.SQS.Model.Attribute();
attribute.Name = "ReceiveMessageWaitTimeSeconds";
attribute.Value = "20"; // 0 to 20 Seconds, default is 0
attributes.Add(attribute);
setQueueAttributesRequest.QueueUrl = queueUrl;
setQueueAttributesRequest.Attribute = attributes;
_sqs.SetQueueAttributes(setQueueAttributesRequest);