Send process to background

Hello list, I am working on a backup system that needs to be called through a webpage to start the process. I am trying to do this on a one-file-only sollution. The thing is, the first request to the site needs to start the backup, but I didn't want to use any command-line tools, since some of our servers rely on safe_mode. Is there any way to send output to the browser on this first instance, finish the request, but keeping the PHP running and making the backup. Thanks. Andre