Store WordPress “uploads” folder on another server

I have four servers and and on one of these servers i have installed WordPress for selling digital files. For security reasons i don’t want to keep files on the same server as WordPress is installed. I want to move “Uploads” folder to other three servers and connect theme to WordPress core. So whenever i upload something via WordPress i want it to be transferred to the second or third server based on file format or file size. How is such thing possible?

P.S: Unfortunately i can’t use Amazon S3.