允许用户使用Ajax下载文件

I am looking for a way to allow users to download a file from my site using ajax. The reason why i need to do this is because the files are quite big (50 megs normally). So when the user clicks the download button it actually looks as if the page is not responding because it has to stream the file from my Amazon S3 to the user.I am looking for a way to allow users to downlo