Setting a php_value via .htaccess is not an option for you, then?
You'd probably have to have some sort of FTP applet (Java, Flash, ActiveX?) that would be loaded on the client side, as you would not normally be able to "pull" files from the web server, but would have to have the client "push" it. (Or if only you or certain people need to use this, you could set up FTP servers on your PC that your PHP script could then access via the FTP functions.)