Background PHP tasks in an ISP environment.

Hi There, Im wondering if anyone has setup some sort of system to enable users to run background tasks in an ISP environment? All our vhosts are locked down from a PHP point of view, but we have had a couple of users wanting to run these sort of things... We thought maybe a way that these users 'submit' a script to be run, which we check over first before allowing, installing the script ins /bin/dir and setting the permissions so they can run it, but not update it? Ideas? Simon