Hi! thank you for you script, it helps a lot in my issue. 
I have had a problem, It doesn't load by default the AWSPowerShell module (you can modify your ps profile for loading it,but...) .
I decide to create an script with params 
* Create CopyFilesToS3.ps1
   param([string]$BucketName="?",[string]$AccessKey="?",[string]$secretKey="?",[string]$region="?",[string]$filename="?")
   Set-ExecutionPolicy RemoteSigned
   Import-Module "{your-path}\AWSPowerShell.psd1"
   Write-S3Object -BucketName $BucketName -AccessKey $AccessKey -secretKey $secretKey -Region $region -File $filename -key $filename
And call it 

    SET @cmd = 'powershell .\CopyFilesToS3.ps1'
    SET @cmd += ' -BucketName "' + @AWSbucketName;
    SET @cmd += '" -AccessKey "' + @AWSAccessKey;
    SET @cmd += '" -secretKey "' + @AWSSecretKey;
    SET @cmd += '" -Region "' + @AWSregion;   
    SET @psCmd = @cmd + '" -File "' + @fileName + '" -key "' + @fileName+'"';
    exec xp_cmdshell @psCmd;