IIRC, Win32 processes do not inherit open files like Unix does. That means when you create the "waiting" sub-process, it won't have a connection to the user's browser.
What you probably want to do is simply turn off caching in the web server (for this page only). What normally happens is the web server intercepts all of the data you are generating and sends it back to the user's browser for you. If you tell the web server not to do this -- your script is taking direct control of sending data -- the browser will see text as soon as you send it. (Don't forget that Perl will also cache your output! See $| for details.) You may need frames, JavaScript or some "meta" refresh tags to get the user interface you want.
